[loldis]

I fly PE/Upper so seat reservation is free, but I would always pay to book if not. Not because I'm worried about sitting apart (DH is grumpy on flights anyway, further away the better some trips ) but because I like to choose where in the plane to sit.

If the third person is a child, they usually do try to seat families together wherever possible. But bear in mind that an airline's definition of "together" is any adjacent seat in any direction, so sitting in the row behind is still considered together.