I'm only 14 so I'll offer some thoughts from the "other side". When we travel as a family (of 4), we'll ask the gate agent if there are empty seats available together, even row 40 toilet seats, so we can sit together, if not, we just make do with what we get and accept that life gives us c**p.
EDIT: One situation where I would gladly move is on a totally empty flight, such as the UA1205 KOA-LAX I flew a couple weeks ago where there were literally three people in the 753's back section:
