really...only when there's a huge dynamic for the amount of effort in creating the sound. like...if you clap your hands...the same amount of work goes in to each clap, but each will sound louder or softer. or if i think a mic "heard" what its recording in a colored way. (not refering to bad positioning)
You'll run into this with voice, clean/prettyclean electric guitar, drums, shakers, tambourines, etc...
typically piano or acoustic don't offer really big big dynamics.
i use my compressor as a means of evening out loud parts....and not to make all song sections come out at -10db on my rms meter