Not entirely sure but check this out [Live] Script RunContext
Only things that are important and give them an advantage in the game. They don’t need permission to click a button that opens a menu
Shouldn’t do. Although your game shouldn’t be structured to where clients are all firing remotes in really quick successions or that will effect performance
" RunService contains methods and events for time-management as well as for managing the context in which a game or script is running. Methods like IsClient, IsServer, IsStudio, can help you determine under what context code is running. These methods are useful for ModuleScripts that may be required by both client and server scripts. Furthermore, IsStudio can be used to add special behaviors for in-studio testing.
RunService also houses events that allow your code to adhere to Roblox’s frame-by-frame loop, such as PreAnimation, PreSimulation, Heartbeat and PreRender. Selecting the proper event to use for any case is important, so you should read Task Scheduler to make an informed decision."
ie. FPS games use run service to constantly adjust the position of the player’s gun so it stays infront of their camera
Kinda. Not difficult to get back up to speed after taking time off