Another bonus of having their own vocal mics will be not being exposed to the major funk (germs, organisms, old beer, etc) that house vocal mics have. Think about how many people have their mouth all over those things day in and day out. At the very least I recommend that singers bring their own foam screen for the mics, but having their own mic is better. For the vocal mic owners out there....If you own a mic like the Shure sm-58, beta-98 (or any mic where the metal screen that contains a small fabric pop filter inside it screws off). That little fabric pop screen absorbs, and the metal gets coated by, smoke from the air, beer (or anything the singer is drinking while playing and singing), germs, etc. They eventually start to smell. Screw them off, stick them in your dishwasher where the glasses go, run a cycle, let them dry overnight and voila! Good as new. A little trick I learned on the road.