May I express a different opinion?
When there are no seating cards, people who don’t know many others at the simcha often feel uncomfortable. Imagine showing up slightly late to a simcha and going from table to table asking if a seat is available. Then imagine sitting at the table where everyone else are old friends, as the conversation flows around you about people and incidents you know nothing about.
The advantage of the seating cards is that it gives the ba’al simcha the opportunity to make sure that all of the guests are put together with people who they have something in common with. For example, an outsider can be put at a table with someone who is particularly friendly and welcoming.