Some couples are deciding to have tall cocktail tables with chairs for that lounge look, but even with this style you should still have some traditional tables and chairs for elderly, disabled and pregnant guests who may have difficulty climbing on a stool.
I've also been asked about not having seat assignments when serving a buffet-style meal. If your guest list is less than 100 that shouldn't be a problem, however you may still want to reserve a table or two for older guests who will need/want a seat. In this situation I would think that your guests would give their seat to a disabled or pregnant woman since everyone is family or a close friend.
If your wedding ceremony will not have seats for everyone make sure to reserve some for guests who may need a seat. You may also want to check with your ceremony and reception locations to see if they are handicap accessible if you do have guests in wheelchairs.