Interesting question. The historical origins of "rules" is very interesting as it often has no relevance with what is happening today. For example, a properly trained dog will always heel on the left. Why? Because you "are" carrying your gun on your right. I'm about as anti-gun as they come, but my 90lb girl always heels on the left.

As for unclipping seated or standing, usually seated. Unless I'm doing a poor impersonation of a track stand and run out of room to inch forward. Then I unclip standing.