Trailers can be a great way to haul stuff and bring the weight down lower, and get most of that weight off the rear wheel.
The bike can easily be transformed from a cargo bike to "regular" bike.
Two wheel trailers are usually but not always wider than a bike with panniers. You need to remember you're towing the trailer and sometimes you might forget and clip post, etc. with a trailer wheel.
Trailers can pull the back end of the bike around. The heavier the load and sharper the turn, the more it can influence the rear.
Sometimes two wheel trailers can tip over from sharp turns, large bumps, etc.