My husband and I learned the hard way about asking carefully what you get for your switch.

We had middle/aisle in the row behind the bulkhead. A couple and their service dog were in that row and asked if we could switch- the wife, who had a degenerative muscle disease, was overweight and needed the armrest up; the bulkhead seats had fixed armrests. Assuming they had the whole row since they had the dog, we moved to the bulkhead. Oops. They had 2 seats and the 3rd was taken by a Mom with a lap child. My husband ended up moving to our original row so he could get his aisle seat (he's tall and needs it), but he had to raise his armrest. The other person who was supposed to be in our original row moved to the bulkhead. Lots of confusion.

Last December I got on a flight from EWR to DEL in Business Class- aisle seat in the middle section. Someone asked to switch so they could be with a friend- they had a window seat in Business, which I actually preferred. But my new seatmate asked if I'd switch AGAIN so he could sit with his girlfriend. What the heck- I ended up one row behind my original seat. I was flying alone so it was no big deal, and was so darn grateful I'd even made the flight I think I would have taken a seat in the bathroom. (My connection from MCI originally posted so late I would have missed the EWR-DEL flight; apparently they commandeered another inbound and we ended up leaving MCI "only" an hour late.) The FA thought I was crazy, but my new seatmate was an interesting consultant who was familiar with my field and my company, so it was a pleasant flight.