Can someone better explain to me how UpdateAsync really works?

I recently asked a question similar to this one but got somewhat unclear answers(In my mind, maybe not yours). So I will now add some more explanation about what confuses me. Here is a script which saves when you leave:

players.PlayerRemoving:Connect(function(plr)--players is: local players = game:GetService("Players")

	local plrInfo = serverStorage:FindFirstChild(plr.Name):WaitForChild("PlayerInfo")
	
	if plrInfo.OwnsTycoon.Value then
	
		local tycoonName = plrInfo.OwnedTycoon.Value
		local tycoon = game.Workspace.Tycoons:FindFirstChild(tycoonName)
		
		tycoon:Destroy()

		local tycoonCopy = savedTycoonsTable[tycoon.Name]:Clone()
		local runTycoonDoor = require(moduleScripts.RunTycoonDoor)
		
		runTycoonDoor(tycoonCopy)
		tycoonCopy.Parent = game.Workspace.Tycoons
		
		if plr.CanSave.Value then
			
			print("Player can save.")
			
			local specialKey = "User_"..plr.UserId
			local moneyToSave = plrInfo.Money.Value
			local buildLevelToSave = plrInfo.BuildLevel.Value
			local purchasedItemsTable = getTableForDataStore(tycoon, plrInfo)
			local mainTableToSave = {moneyToSave, buildLevelToSave, purchasedItemsTable}

			local success, message = pcall(function()
				
				mainDataStore:SetAsync(specialKey, mainTableToSave)
				
			end)

			if success then
				
				print(plr.Name.."'s data saved successfully")
				
			else
				
				print(plr.Name.."'s data failed to save successfully")
				
				wait(15) 
				
				local maxAttemptsAllowed = 3
				local saveAttempts = 0
			
				repeat
					
					saveAttempts = saveAttempts + 1
					
					local success, message = pcall(function()
				
						mainDataStore:SetAsync(specialKey, mainTableToSave)
			
					end)
					
					if success then
						
						print(plr.Name.."'s data saved successfully on try "..saveAttempts)
						
					else
						
						print(plr.Name.."'s data failed to save successfully on try "..saveAttempts)						
						
					end
					
					wait(10)

				until success or saveAttempts == maxAttemptsAllowed

			end
			
		end
			
	end
	
	wait()

	local plrFolder = serverStorage:FindFirstChild(plr.Name)
	
	plrFolder:Destroy()
	
end)

local mainGameLoop = require(moduleScripts.MainGameLoop)

mainGameLoop()

In an answer to the previous question incapaz said when quoting the wiki: "Retrieves the value of the key from the website, and updates it with a new value. This function validates the data and must therefore be the standard function to edit data when there is a chance more than one server can edit the same data at the same time.". There is a chance that my script above will update the datastore from two different servers. Especially if I decide to increase the wait between retries. How does UpdateAsync defend from that? The other person who answered my question said: "UpdateAsync is generally considered better because it's a bit faster than SetAsync. It also allows you to look at the old value before you overwrite it with a new one just in case something "doesn't seem right".". How is UpdateAsync faster? Finally, how would it know if something "doesn't seem right"? I am so confused. Help would be much appreciated. Thanks!

If it helps.... If the previous value of the key is important, use UpdateAsync. Using GetAsync to retrieve a value and then setting the key with SetAsync is dangerous because GetAsync sometimes returns cached data, and other game servers may have modified the key. Mind that there are limits that apply to this. However, if more than one server will likely be writing to this key, it is recommended that you use UpdateAsync instead.