It's always been amusing to watch the band set up. The guitarist brings his amp, a few pedals, and maybe a couple of guitars. The bass player brings his instrument, and often his own amp. The drummer uses the church's drum kit, but he brings his own sticks and takes the time to tune and position the drums to his liking.
But the vocalist just uses whatever mic is handed to them.
My experience has been that the choice of microphone for the vocalists, especially the lead vocalist, has a substantial effect on her sound in the house, her intelligibility, and even her confidence in front of a crowd. Using "whatever they give me" would be like the the guitarist playing "whatever guitar they hand me," whether it's a Fender Squire or a Paul Reed Smith Custom 24 guitar, or the sound guy saying, "Yeah, whatever. Behringer, Midas, Yamaha, Digico: they're all the same."
The point: if you're a vocalist, find a mic that really lets your voice give its best in your facility. If you're the sound guy, then give real thought to what mics sound best on which vocalist, particular the main vocalists. Try out some new ones if you need to, and teach your team that "This is John's mic!" Or encourage John to buy his own vocal mic.
And of course, audio engineers love working with untrained vocalists, who sing away from the mic, lean into the mic for their loud notes, and cup the grille. The reality is that a good sound system will clearly amplify whatever sound (good or bad) that the vocal mic picks up. It is not to the vocalist's advantage to send a poor signal to the sound system.
Audix created this video, and they make some excellent vocal microphones (and some amazing instrument mics), including some at modest prices. Of course, they use Audix mics in these brief clips. But the techniques are appropriate for any handheld vocal microphone.
Note: this post contains a video clip. If you're having a hard time seeing it, click on the title ("Vocal Microphone Technique") to watch the video on the post's home page. And if you want to share the video with your vocalists, use this link: http://j.mp/VocalTechnique.