I was wondering the same, but evralia has explained it pretty much. Actually I never thought about letting UA/Corruption tick off when they are buffed with the best procs. It really does make you think, and it helps to know the value of each proc and have them displayed clearly so you can see just what you're buffing your dots with.
The balance is refreshing your dots as close to the 50% mark as you can whilst buffing them with procs. Sometimes I'm in a situation where I have 10 seconds left on say, my DMC ICD, but to get another full MG out, I'd have to let the dots drop off. Always mentally note just how supercharged your dots are at any one time and you will begin to manage your own priorities in a sense.