Useful functions to hook for internal hack

Hi guys,

I've been reading around the work done on hacking CSGO so far, and there's quite a mess of information. It seems that most of the stuff built for it is "external"? In other words, the code behind it isn't designed to be injected - instead it reads/writes memory addresses as another process, and renders on top of the game. That's what I gathered with the bunch of mem.read/write calls in there.

I'm looking to build an "internal" one - one that uses the game's engine to recognize models, render, etc. (Different ESPs kind of thing is the end-goal, but I'm not looking for a finished project.) So that makes all those examples useless - and they seem to be most of the examples around the place.
After a day of reading around what I'm still unsure about is which functions in the game are the interesting ones - both to hook, and to call for parsing through entities and rendering on top of them. Last time I did this it was COD4, so I'm guessing it's similar for CSGO.

The only one I've seen come up quite a few times was this:
I've seen people trying to hook this all over the place, but not why. Hooking it is easy, but what is it useful for? What does it do? Is that the right starting point? Is this where I should be getting access to world entities (somehow), parsing them and rendering?

Thanks for any insight you guys can give.