Many of my successes of fishing a dry-dropper combo gets the fish to take a look at the dry, refuse it then eat the dropper on his way back to his hole. Especially Grayling!

Typically, if I fish dries, I just fish dries, and don't worry about the dropper. Though I will often times fish a pair, a larger fly and a smaller something that is difficult for me to see on the water heh. Did that once, and turned my head for a sec, looked back and my bigger dry was skating across the water and a fish then struck the skater... which was a caddis dry. To this day, that hookup, is probably one of my top 5.