I own a TC VoiceLive. I use it at our gigs because unfortunately, I am the only one who can sing. My band mates are great musicians, but don't have a voice.
I just dial up the song, press a foot switch, and it's like have 2-4 of me in harmony.
I only use 2 part harmonies for most of our songs. One nice feature is the harmony hold button, as long as I hold that foot switch in, the box will sustain, oohs,etc. while I sing lead over them.
I don't use the pitch correction.