I mainly use mine as the bottom layer when Icebiking. I do take a pair along on tour. Two reasons really:

1) It's nice to have something comfortable under normal shorts when I go check out a museum or explore a city.

2) As a precaution against sore butt. I haven't needed them for this yet since I have my great Brook's Champion Flyer saddle but there's no rule against wearing a pair of the padded underwear while wearing a pair of padded bicycle shorts. Double layering. This is sometimes a good technique early in the mountain biking season when your butt hasn't yet hardened like it should!

~Jamie N