Topher Welsh has a quick tip on creating "super tight" garbage mattes to aid keying. He uses a basic After Effects color key like Color Range then applies the Simple Choker filter with a negative setting, expanding the matte to let an advanced keyer like Keylight to work more subtle magic. This technique that can also be found in Making It Look Great 5 with Maltaannon.
The technique is inspired in part by an older video by Aharon Rabinowitz, Super Tight Junk Mattes which used Auto-Trace and the Simple Choker to refine garbage mattes (project files are still available at Cow). Aharon similarly leverages convenient Red Giant filters in a more recent tutorial, RGTV Episode 4: Better Compositing Techniques.
Also there's no reason you can't use a copy of the matte with Simple Choker to do a choke for a hold out matte to preserve the keyed subject (as seen in Commotion Complete by Matt Silverman and recent keying training from Toolfarm). Here's Aharon's older tutorial and the new one by Topher: