Some simchas that I have gone to have made interesting arrangements. They had special tables listed as “family X” and family “Y” and several tables blank on each side. That way the rebetzins could sit near each other, planned, as they sat at the table marked “family” (they were told to) and all the family and friends from out of town were able to sit near each other without feeling weird.
The problem with making seating arrangements is that there are only so many seats at a table, and it is weird to have half a table. Many times there are “mixed tables” of different groups. The guest feels weird that the host didnt think about them that highly that they arent seated with so and so…
Shouldnt simchos be a time where we show ahavas chinam and try to befriend different people?