To grid? or not to grid?

okay sorry for the lame title, but since this isn’t really a direct question, i might as well turn it into a fancy name.

so what i have bin wondering for quite a while now, is when you should use a grid (either 2D or 3D).
on my YouTube channel i make tutorials for beginner programmers who are using Stencyl (which is a great program if you don’t have a lot of coding knowledge btw. my channel is >> https://www.youtube.com/user/ArtificialStudioInfo)

on my channel i was doing a tutorial serie in which i was explaning the basics of an RTS game such as Age of Empires. in this project i used one big 2D array to store all the buildings that were placed, and also saved this complete grid with all the data for each building (position, damage, upgrades etc. etc.) if the player wants to save his game. however, i dont know if this is the most efficient way of doing so.

so again, my question is:
when should i be creating a 2D or 3D grid, and when not.

cheers!

Grids are very important to create uniformity. This uniformity can define level building, enemy attacks, player movement. It’s really endless.

I think grids should be used if they are needed. If not, then don’t. There is no golden rule. However, being aware of thier usefulness is very beneficial than not.