I personally DoT and spread when I get time. The further along you get, the harder it can be (depending on the mobs). In Stone Vigil, I was able to contribute damage through DoTs up until the start of the final boss. Once we started and I did my initial DoTs, it was full time healing. Part of this was mine, and the tank's, inexperience with that boss. (both on run him 2-3 times tops)