I'm surprised that I could not find a thread on this so apologies if I missed it. What are others' experiences about the "seat allocated at check in" and best time to check in for it?

I used to think that it was a case of try to check in as late as possible as they'd first allocate rubbish seats to hope to sell the good ones for a fee till the last minute but I am no longer sure. Conversely, I used to think it was random in terms of what seat you get within a row, but more recently I have had the impression that at least on some flights they seem to give couples window and middle and single passengers aisle (which isn't good for me!)

I thought it would be good to share experiences!

For reference, I take upfront seats on many flights when I want the proper hand luggage (comfort of a good seat comes mostly as a bonus), but I find that prices seem to have increased a lot for this recently so don't always do it if I am on a very short trip for which the backpack is enough. I also find that on many of my flights, U2 seems to have reduced the upfront area by one row which surprises me, and as a result, there have been times when only a middle seat would be available there in which case I sort of object paying.