I use it on some individual tracks. Sometimes. Depends on what it needs. It can help bring something forward in the mix that might otherwise get to bright. Just to smooth out some transients. I also use it on the master bus for an overall smoothing and gluing of the mix. The key is the level going in. Not too hot and not to low. You kind of have to use your ears.
I use a WAVES Dorrough meter before my tape sim plugs. If the level is right there, is usually right for the plugs. That's pretty much the case with all the UAD plugs I've found. They don't like a really hot signal.