are there upsides/downfalls to single-axle TT's?

I've owned small trailers in both configurations. They both towed well. Obviously the single axle has fewer tires and wheel bearings to deal with. In the past, some small dual axle trailers came with tiny 13" wheels with no room to upgrade. This could impact the ability to use top tier tires. Moving to a smaller trailer opens the door to molded fiberglass, far superior to other construction methods with regard to durability, IMO.