"How could this possible be better than using git and having a sane version history."
For starters, we have really good collaboration. Someone could be writing code, someone else notices fucked indentation or syntax, an can fix it on the fly while explaining what's going on.
"And if you are what possible advantage is there for everyone logging into one system - and you being local"
Most of my devs are in other countries. Waiting for everyone to do their thing, submit, and have to dig through shit to see what does and does not work eats too much time. Time zones are a fucker like that.
To boot, my system is the server system, so having me be local and able to test live is what makes things run smoothly.
The only one piece of documentation we need is the design documentation. Everything else is a waste of fucking time, especially when a new client upgrade could force us to re-write half the code base in the first place (like last night's upgrade forced us to have to scrap and re-write half of the initial framework.) As long as we have that design documentation, if shit changes, we still know what needs to be done and can do it, instead of having to go looking back through code and go "Okay, here can we make changes here?" That's sloppy as shit and leads to security problems.