Hi Leah,
I do not level until I have my slides out if that is what you are asking.  Here is my reasoning.  First, that is what my directions say and, second, I was in a site that was very far from level, I put my slides out, opened  a basement bay door then leveled...once leveled, I couldn't close my basement door because of the torqued frame (not close!!!).  I sure wouldn't want to put slides in or out with a frame that severly torqued.  I'm sure this response will draw additional comments.  I hope this addresses your question.
Tim