Compression is good for 90% of the singers I've got one gal that drives me nuts when I have compression on and still don't have it figured out. I have another one that does broken wing and when she reaches the the flyyyyyyyyy part at the end my mixer widens about 2" every light comes on and the speakers start walkin towards the door.There is a difference between compression and limiting but compression with her at least keeps my speakers inside.
Also like to run the gate high and it helps to eliminate unwanted noises like getting mic out of holder etc.
It also helps with the folks that like to walk up and scream in the mic.
I run all my music thru a nanocompressor and duck the music to a lower level with the announce mic. Works great with a wireless. Then I run it thru a compressor for limting .It helps somewhat with different cd audio levels.
All in all it's another one of those things that when they are workin right you wonder how you ever got along without them and when they don't work drive you absolutely nuts.