Since we are suppose to put in a "note" or say something about the changes we make with a reference, I put the "note" or info in the bio, add the reference, put in the explain box, Add the marriage info and reference, save it, then go back and edit the marriage information...if you put a explain the change box in the marriage portion, I would be concerned that people won't put in the "note" and reference, leaving the profile manager to try to find where they editor found their information. I don't know about everyone else, but any changes made to the profiles I manage, I always make sure what they put in is a valid change with the appropriate reference (those little "citation needed" flags bug me, and I feel it's kind of rude to just make the change without including the info and reference in the bio, because it creates more work for the profile manager who may not have access to what you found on Ancestry.com or the others, so how are they suppose to cite the reference (if that's where you found it). Just my opinion based on my own experience with the profiles I manage.
(Please forgive any typos in this answer, I'm tired)