Well, if you're towing a 15 pound trailer with 35 pounds of gear vs. 50 pounds of gear on the bike, that's 15 pounds of stuff you don't have if you absolutely need it. On the other hand, if all you need is 35 pounds of gear, then that's all you need and you don't need the trailer.

IMO: if you're touring, it doesn't matter one way or the other.