I have the Waves SSL Buss Compressor (The Glue), and use it on every mix.
If you have the G channel, as far as using the Buss comp on individual tracks, there is no need since you already have a comp section on the g strip, and a great comp section at that.
As far as what makes the SSL BUSS comp better for the master buss, is it's character and the way it gently glues the mix together. It isn't a fix a bad mix band aid. It is a comprehensive final cohesive tool to glue the mix together. Experiment with it and try it out on your mixes, it's software so it doesn't cost you anything to experiment with it.
I have found that one of the keys to using the SSL Buss Comp on the Master Buss is to shoot for a 2 to 4 db of compression using your threshold control, with a ratio on 2. fast attack (.1) Medium release (.6). The analog button as you probably know. adds a bit of noise, which is a matter of preference and individual choice, I always keep it off. That's just a starting point for you to experiment, Hope that Helps.