How to properly use the methods Roblox has provided, namely :FindFirstChild() and :WaitForChild()?

In this question, I will be focusing mainly on :FindFirstChild() and :WaitForChild(). Often I am confused and uncertain as to whether or not I should use one, or neither, of the listed methods. Because :FindFirstChild() returns nil when the object is not found, I am sure that I should not use it like this:

local box = game.Workspace:FindFirstChild("Model").box

Because :FindFirstChild() returns nil, the variable definition will error. If I am doing it that way, why not just do:

local box = game.Workspace.Model.box

I can see using :FindFirstChild() if the name has spaces, but I could just do something like this:

local box = game.Workspace["Box Model"].box

If I want to use :FindFirstChild() without it erroring, I end up needing to do checks all along the way like this:

local boxModel = game.Workspace:FindFirstChild("Box Model")
if boxModel then
	local boxHolder = boxModel:FindFirstChild("Box Holder")
	if boxHolder then
		box = boxHolder:FindFirstChild("box")
		if box then
			-- code
		end
	end
end

That method just seems extremely inefficient. Another thing I have done to be careful is this:

local players = game:GetService("Players")
players.PlayerRemoving:Connect(function(player)
	local canSave = player;FindFirstChild("CanSave")
	if canSave and canSave.Value then -- canSave is a BoolValue
		--code
	end
end

There must be a better or more efficient and intelligent way to go about using :FindFirstChild().

I have been told :WaitForChild() is for the client when waiting for things that have not spawned in yet. This makes sense, until I talked to someone on the discord (this is the code that was in the discussion):

local text = script.Parent 
local players = game:GetService("Players")
local player = players.LocalPlayer
local contentProvider = game:GetService("ContentProvider")
local loaded = player:WaitForChild("Loaded")
local connection
while contentProvider.RequestQueueSize > 0 and not loaded.Value do
	for i = 1, 3 do
   		text.Text = "Loading"..string.rep(".",i)
    	wait(.5)
	end
end
local backpackDisplay = player.PlayerGui.StatsGui.Backpack.Display
require(backpackDisplay) 
text.Parent.Visible = false

The backpackDisplay was not working correctly and I was uncertain why because the loop should have waited till everything had loaded in. After asking on the ScriptingHelpers discord I was informed that RequestQueueSize did not count GUI stuff, but only assets. In order to fix this the person recommended using :WaitForChild, which made sense. I then became confused as to where I should place the :WaitForChild. I tried doing this and it worked:

local text = script.Parent 
local players = game:GetService("Players")
local player = players.LocalPlayer
local contentProvider = game:GetService("ContentProvider")
local loaded = player:WaitForChild("Loaded")
local connection
while contentProvider.RequestQueueSize > 0 and not loaded.Value do
	for i = 1, 3 do
   		text.Text = "Loading"..string.rep(".",i)
    	wait(.5)
	end
end
local backpackDisplay = player.PlayerGui:WaitForChild("StatsGui").Backpack.Display
require(backpackDisplay) 
text.Parent.Visible = false

I went back and asked the guy who answered who answered my question originally and he said that was all that was needed. Why did I not need to do:

local backpackDisplay = player.PlayerGui:WaitForChild("StatsGui"):WaitForChild("Backpack"):WaitForChild("Display")

or, as one of the options I listed with the :WaitForChild(), why not do this:

local statsGui = player.PlayerGui:WaitForChild("StatsGui")
if statsGui then
	local backpack = statsGui:WaitForChild("Backpack")
	if backpack then
		local display = backpack:WaitForChild("Display")
		if display then
			require(display)
		end
	end
end

All of these questions berate me whenever I am writing scripts involving objects, which as you may guess, is pretty much every time I script in Roblox Studio. Any help would be much appreciated. Thanks!

I, myself am somewhat of a newbie when it comes to built in functions of Roblox Lua, but I think one of the purposes, or at least one of the ways I use :FindFirstChild() is when there is a bit a latency, or if I am waiting a set about of time after an event to do something, say damage a person with a sword after an animation has played, or checking if the player has a creator tag in them when they die: Ex1:

game.Players.PlayerAdded:Connect(function(plr)
	plr.CharacterAdded:Connect(function(char)
		local creator = plr:FindFirstChild("creator")		
		if creator then
			if creator.Value and  then
				local leaderstats = creator.Value:FindFirstChild("leaderstats")
				if leaderstats  and leaderstats:FindFirstChild("points") then
					local points = leaderstats:FindFirstChild("points")
					points.Value = Points.Value + 1
				end
			end 
		end
	end)
end)--the creator tag is an object value and the value of it is a plr object

Ex2:

--one script
wait(2)
local thing = Instance.new("Part")
thing.Parent = workspace
thing.Name = "brick"
--another script
local thing
repeat
thing = workspace:FindFirstChild("brick")
until thing ~= nil--not needed but to prove a point

This brings me to the second usage of FindFirstChild, it allows you find the child of some object without throwing an error if it isn't there, say I have a typo on a bit of code like this :

local a = Instance.new("Part")
a.Parent = workspace
a.Name = "thing"

if workspace.thkng then--throws an error

end

alternatively, if I have a typo on a bit of code like this

local a = Instance.new("Part")
a.Parent = workspace
a.Name = "thing"

if workspace:FindFirstChild("thkng") then--doesn't throw an error
	print("yay")
else
	print("uh oh")
end

In this aspect, it is superior to WaitForChild and the **.**as it doesn't infinitely wait for "thkng" and allows the rest of your script to go on undisturbed.

--if WaitForChild() is used without a timout argument
local a = Instance.new("Part")
a.Parent = workspace
a.Name = "thing"

if workspace:WaitForChild("thkng") then--waits forever and doesnt let the rest of the script run
	print("yay")
else
	print("uh oh")
end

However, In some areas, WaitForChild() is better, such as trying to get the humanoid of a player character in a local script;

local humanoid = game.Players.LocalPlayer.Character:WaitForChild("Humanoid")

or in the script i mentioned earlier on

--one script
wait(2)
local thing = Instance.new("Part")
thing.Parent = workspace
thing.Name = "brick"
--another script
local thing = workspace:WaitForChild("brick")