The Sky's the "limit(er)"
In our classic rock band, I often use a Yorkville powered mixer with 2 Peavey SP 5 Mains (just purchased) and 2 Yorkville 12" woofer / horn monitors. A friend sold me his new Alesis 3630 for a steal, and although I knew very little about compression functionality and settings, I decided to integrate it with my system. The 2 channel functions are perfect for adjusting the mains (mono) and monitors (mono) seperately.
At our next gig, I wasn't too happy with the sound, I had used the -10 DB setting since the manual recommends that for most applications. However, as soon as I switched to + 4 DB, I had to reduce volumes and gains, since my system sounded like the 1812 Overture! Feedback occurrence was substantially reduced, even when the vocalist grabs his mike at the top, and the vocals now sound full and ballsy for both monitors and mains. I can even hear the mains in addition to the monitor!
I'm still fine tuning some of the settings, and our lead vocalist is now adamant that we use the compressor, since his vocal style now depends on it - he can growl, scream, sing all he wants, the compression both gives him the freedom, yet also keeps any peaks in line.
Great product, especially for PA applications!