It's a common question - to assign, or not to assign. Most of the time, my answer is YES, but it's really not a one-size-fits-all question. Here are some Pros and Cons to weigh as you consider assigning seats or assigning tables for your guests at your wedding reception.

CONS:

It's certainly more work for you, as you'll need to spend quite a bit of time determining and organizing the best placement for each of your guests.
Changes are a pain. It is almost guaranteed that you'll have RSVP changes late in the game - even the day before the wedding. Which means those assignments will need to be redone.
Assigned tables might be a bit more formal than what you're aiming for, depending on your style (though assigning tables is less formal than assigning seats).

PROS:

Groups get to be together. Your guests will arrive at the tables at different times, as some are involved in post-ceremony pictures. Assigning tables ensures that those families/groups that want to be together, will get to sit together.
It's easy to communicate dietary concerns to the catering staff ("one guest with a peanut allergy at table seven").
There's no need for extra seats when you assign tables/seats. When you do not assign, guests will skip a chair between groups (like we do at movie theaters!), resulting in an unused excess as most guests will have at least one guest with them, rendering those single seats uesless. When you assign tables or assign seats, you eliminate that excess, which will save you on the costs of tables, chairs, place settings, linens, centerpieces, etc.
With a spot reserved for them, your guests feel welcomed. It's obvious you've put a great deal of intention and thought into their placement, making sure they're with people they know or would enjoy getting to know - and they appreciate your concern!
Guests don't worry about someone taking their seat when they leave to go to the bar. I can't help but cringe when I see someone "save" a seat in a gorgeous ballroom, by tilting a chair! Not only does it look tacky and create the opposite of a welcoming atmosphere, but it will trip some poor unsuspecting passerby. Nobody wants to see Grandma trip because her dress snagged on a chair leg jutting out from a table!