If you are considering two similar trailers - one with double axle and one with single axle, examine the specs. You'll find that the double axle trailer has a much higher GVWR, which generally translates into a much higher cargo capacity. Yeah, the additional axle adds to the curb weight, but it buys you much more cargo capacity.
When I first started shopping for a small-ish trailer I was pretty sure I wanted single-axle. I didn't like the idea of buying and maintaining twice as many tires. But when I started really thinking about what that extra axle gives me in terms of cargo capacity and increased stability, I changed my mind. You don't have to replace tires that often.
-Speak