There are numerous reasons for mixing signals with no reverb. My setup has effects bulit in to the kb and mic sp I'm a good example of someone who doesn't need it built in to the mixer.
DJs, don't need it.
Public speakers don't need it.
Many jazzy singers use very little or none. In fact, there are definatly times when I prefer to sing "dry". In the right setting ... intimate, small, quiet .... it's more authentic than a digital reverberation at a volume that too low to be realistic. Natural room noise is all you need sometimes.