1.) Hitching a trailer is a hassle, especially if you're trying to hook it up by yourself. 2.) Storing a trailer can be annoying, depending on style, and some HOA's or apartments don't like the idea of one sitting around in plain site. 3.) The shape of many trailers is not as conducive to some tasks. An example: a lot small/medium trailers are square or enclosed. If I want to haul some 8 foot (or 16 foot if you have an extended-bed truck) 2x4's home from Home Depot, I can throw them in the bed of my truck with relatively little difficulty. There are many trailers that don't work for something like this. In fact, I can't think of any trailers that would work with 16 foot boards..