It runs them as needed. If there is a lot of file activity or if the date conditions warrant it, it will run. Otherwise it won't. Version 3 is fairly well tuned to run specifically when needed (it has a whole engine just to calculate/predict that). If it is running a lot, that usually means it has to (i.e. there's a ton of file activity keeping it busy) or there's a bug (in which case, you need to turn on debug logging and send me the logs).