I don't do it much, particularly when playing Bluegrass or Old Time string band music with other instruments, where you pretty much have to stick to traditional keys.   I must confess that after I got the "bass banjo" case I was curious as to whether I could do some "bass banjo" and looked for some situations where it worked. However, when accompanying mostly vocal music I'll play all over the place - wherever I can make c or g shape chords fit the singer's range- so it's not that uncommon to play with no capo in that situation.   I think Seeger did pretty much the same thing since he didnt do much bluegrass - just put the banjo wherever G or C matched his somewhat limited vocal range. He wasnt into the "high lonesome" vocal sound so the lower frets gave him a lot of flexibility in matching his voice. But I dont do much of that any more - mainly play guitar these days - banjo gives my wife "Deliverance" nightmares