I whack the master signal through an outboard compressor sometimes, to get a guage of what the track will sound like after someone more skilled than me gets their hands on it.

But I only do it for guidance and reference. Sometimes your mixdown sounds a little flat, and you need to have an idea of what it will sound like beefed up.
Just best to leave the beefing to the experts.

Another vote from me for Chris in this respect. Top quality service.