Watch the Using a Capo online guitar lesson by Cathy Fink from Clawhammer Banjo: Beginner Module 1
The capo easily allows us to play in diferent keys-moving the capo up the neck changes the key by one hal-step. In G tuning, cap on the 1st fret and you'll be in G#, 2nd fret in A, 3rd fret in Bflat. I use all the keys for singing.
You'll find banjo tunes/dance tunes in this tuning to typically be in G or A, but remember that the 5th string has to follow and match the 5th fret of the 1st string.