This all depends on whether you want to "feature" the harmonies or not.
Check out "Nightengale" on my demo page
www.boydsongs.com - it showcases the harmonizer as if it were the Manhatten Transfer arrangement.
It can be Sooooo effective when used correctly.
The most important thing for me, is to "THINK" like a vocal arranger, and sing accordingly. You need to phrase differently, and approach some things with a communal effect. ANYthing can be overused, but in MY case, the harmony sound has become a trademark.