For example, I want to destroy a certain part of the map to reduce lag but obviously not destroy that part of the map for other players. How would I go about doing this?
Destroy the part via local script, you may need to use RemoteEvents
Just do it in a local script. But keep in mind that local scripts do not function in workspace or server run areas etc. I would place this in StarterGUI:
local part = workspace:WaitForChild("ThePart'sNameHere") part.Transparency = 1
You can do much more than set local transparency. All I will say to you is that everything run in a local script, is local. That is why it is called a "local" script.
I hope I helped.