very bad idea if you're singing. compressed monitors lead to pushing too hard and blowing your voice out. (FWIW they also lead to feeding back monitor wedges.)For me compressing/limiting the IEM signal is key. You will hear the audience in the gaps between songs better, solely through the audio picked up by vocal and drum mics (providing you have those in your mix). The signal when you are playing will also sound warmer and more natural.
i do find that some compression on my bass made for a better IEM sound, but i did that on the bass signal itself, not my IEM mix (i sing backups).
this is quite different than a safety brick wall limiter on your IEMs; that's a good idea, but only if it's set to not kick in at normal levels.