In "Angel One," Commander Riker dons the clothing of Angel I before negotiating with Mistress Beata.
He tells a snickering Deanna Troi and Tasha Yar, "On Kabatris, I had to wear furs to meet with the leadership council, and on Armus IX I wore feathers."
Is it basically an issue of appealing to the wishes of his audience? Or is there a reason why an away-team leader may wish to don the native clothing?
This issue doesn't come up very often, so I assume that these particular worlds were really strict and had high opinions of themselves.