I've only ever been to two weddings in my life, one where the seating was assigned and one where it was not. Honestly, people ended up rearranging the seating anyways at the wedding with assigned seating. The open seating wedding worked just fine. It was made clear that the front two tables were for the bride and groom's close family and the rest of us just made friends.
If you do end up assigning, places like TheKnot have programs to help you sort everything out.
If you can take the time to do assigned seating please do it! It is very important and allows the seating to be organized and run smoothly. The last thing you want is a family or group of friends who arrive late and find out they have to split up their party because their is not a full empty table left for them. Many times (and this does happen), they will request another table so they can sit together. Now what do you do......you have no specialty linen, seat covers or an extra centerpiece. I know how tedious assigned seating lists can be but it's worth it.