I can't say enough about the EBS comp pedal.  It tightened up my sound, and it gives a nice boost (if I want it) to my weak-signaled EUB.  You can certainly use it as an effect, although I am not personally fond of that sound.  I suppose it keeps my rig safe from harmful transients, but that's not usually a problem, anyway.  I simply like the tight sound.  I tried one of those half-rack space DBX units, and was disappointed.  The EBS sounds great, though.  I am actually thinking of putting another one in my pedal board, simply for the EUB, so that I don't have to get on the floor and adjust the boost every time I switch basses.
 
www.andycalderbass.com

I used to run an Alesis 3630 dual comp. My SWR has one built into it, but I never run it. Never had the need to. I'm with Dave and Joey here, I have a huge amount of dynamic control in right hand and compression can alter this. I don't discourage using one but compression is just not for me. But now for guitar I love compression, especially when there is a need for an overdriven hard but smooth sound.

Exactly, Olie.  Think of Brian May's lead tone without that 'pulled' sound of a hard-knee compressor.  You hear that effect a lot in country music on clean electric tones as well.
 
J o e y

@88persuader: That's exactly the way, I feel about it...
 
Gruesse, Pablo