Everything in life has its pros and cons. A trailer is no different. I have a 7' x 16 trailer with AC, 110v / 12v throughout, am/fm, flat panel t.v. with satellite, mini fridge/freezer, hot dog/hamburger grill, microwave, air compressor, foldout starter table on the door and most importantly a very loud alarm with flashing lights! It is wired for local and generator power. It pits 3 comfortable but we squeeze 4 sometimes. The little inconvenience of 4 people helps alot with the fuel bill when we go to away races.
That is a critical point, if your gonna look at buying a trailer, but it large enough that you can bring some buddies with you to help offset the fuel bill. Also, no matter what length you get, spring for the 8 foot wide model. Doesn't seem like much more space, but it makes a world of difference.
I really enjoy it, especially when it starts to rain. I don't have to worry about my things getting wet. All the carrying my gear around from my garage to the car, from the car to to the track and then reverse everything got old. Since I bought the trailer I really enjoyed the hobby much more. One the down side, it does separate you a little from most folks since you tend not come out when it is really hot outside. It isn't so bad because you get a lot of your buddies visiting. As far as trailer not being allowed, yes I have heard of that, but haven't run into it yet. I normally disconnect the trailer from the truck at the bigger races and park my truck elsewhere. This frees up a lot of space for others.
I went in half with my brother in law on the trailer since we are both avid racers for years. IMO, the trailer has more pro then cons which is why we went with it. Sits in my garage plugged in. Also perfect for when I am home and want to work on my cars. Just open the door, turn on the AC and go to work.