We put in a deck a few years ago and had to get a zoning variance. What a nightmare and long and expensive process. Had to go in front of the zoning board multiple times to get them to approve it. The whole process took like 6 months.. They also made me spend a few thousand on a survey before and I after I built the deck.
As much as a pain it was now a days you need to do it. My neighbor built an addition without permits like 5 feet from the property line where we have a 25 foot zoning setback. The town caught it and made his life a living hell. He had to spend big money on lawyers as the town wanted him to rip it down. Also, now a days everything is checked much more thoroughly when houses are sold. If you have an illegal addition, deck, shed, etc you can almost guarantee it will be found when you try and sell.