We did self-seating, and it worked out great. Many of the tables were exactly what we would've chosen, like "spouse's work friends", but it also let us avoid sticky situations like "number of aunts and uncles don't easily divide by the size of the tables". We wound up with great hybrids like "several cousins but also one aunt and uncle".

Later I learned that decades earlier two brothers had stopped speaking forever over a misinterpretation of the searing arrangement at a family event - it was meant to be a table of "close family", but the attendee assigned there thought it was "the kids' table".