Depends on the situation. If the payment was going to be split I think usually it would be something I arrange ahead of buying. Like let’s say several friends want to go we might split the fee for a table. Or, if I buy a table and basically advertise to sell the seats to people interested in coming, realizing I might get stuck paying for the whole table if the table isn’t filled up.
If I invite someone to attend, then I’m picking up the tab and they can donate extra to the cause if they feel so inclined, which I think is a nice thing to do, even if it’s just $20, although the meal was likely $50—$100.
The person paying for the table maybe gets a tax write-off and so it’s not just the donation, but also a side personal benefit that the tickets aren’t costing them as much as face value.