Of course, one could also set the priority in the task manager. I don't know if it's the same at your's, but sometimes I need the full ressources of my PC, not only CPU, but also nemory and network bandwidth.
Our music is stored on a central PC and during conversion, all network interaction with that PC becomes terribly slow so that it takes minutes to do easy things like copying or deliting files on it.
And the only alternative is, like I said, to abort