Ed,
My primary concern has always been vocals. even when we had small bands years ago ... it was imperitive that the harmonies be tight. I'll hire a great singer that plays "ok" before I'll hire an "ok" singer that plays great.

With THAT said:
I often invite area performers up on my stage to sing and I love providing a 4 part vocal group behind them. We do lots od DooWap, and 4 freshman type arrangements .... even if the original song was not done that way. I stress the vocals on every number, and consider the harmonizer to be an invaluable tool.

Because of the importance of the vocal arrangements - I use my right hand to trigger the chords that are harmonized so I can add the finer nuances and passing tones needed for that fat, Manhatten Transfer sound. I pattern my vocal arrangements after groups that really feature the harmony as ONE, and not as backup. Like the Carpenters, the Beatles, The Eagles, 4 fresman, 4 Aces .... that sort of vocal styles.

Many new users tend to OVERuse a harmopnizer, and it takes away from it's effectivness, but when used with taste and moderation .... it's a great way to avoid the boredom of working a solo (or small band) situation. Even now, as a soloist I do Beach Boys, Mills Brothers, Andrews Sisters ..... It's a great addition. And if you do dance music - try the "octave down" voice on a Barry White or Lou Rawls tune. The crowd eats that stuff up.

Good luck in your journey to vocalLand !