Clearly yes. Families do need to sit together - or, rather, young children need to sit with a parent or other responsible person. (Yes, I know children travel unaccompanied, but they shouldn't have to if their family is on the plane. And very young children can't be separated from their family anyway.) And there will be some vulnerable adults who will need to sit next to the person that they are travelling with.

As for the rest, it's often nice to sit with one's travelling companions, but rarely essential. I remember, for example, a couple making an awful fuss because they couldn't sit together on a flight from London to Vienna. As the flight only lasts two hours or so, I couldn't see that it ought to be such a major problem.

Perhaps I'm prejudiced though. I used to travel sometimes with a more senior work colleague who always insisted that we should sit together "so we can go through some of these papers and documents". Achieving this requirement that we sit together always involved my waiting around for him so that we could check in together. Anyway, I'd get on the plane all primed for a work session. My colleague, meanwhile, would get distracted by the menu or the wine list or the view out the window, eat whatever meal was due, and then fall asleep. So much for working on the plane!