Not being snidey about those who choose to do so, btw - I just genuinely have never understood the necessity. At my own wedding we let guests sit wherever they wanted (aside from the top table, which we did the traditional way) and it felt so much easier than trying to plan it all out.
A relative is currently wrangling with the seating plan for her own wedding - mustn't put this person next to that person as they don't get along, etc - and it got me wondering why people bother.
Am I missing something? (Not trying to say either way is right or wrong, btw, just saying DH and I found it easier to not have one.)