I re-use once or twice depending on how dirty they are. If they are a PIA to clean they get tossed. I reseal often as well. I.E., I pack individual portions in a bag. Remove a serving or two and reseal.
I often pre-freeze individual serving sizes, wrap in plastic then vac seal. This means the bag is easily re-used without cleaning or a light rinse.
When I heat up something in a bag it depends on how messy it is.
Also when storing something that's dry like nuts, flours, etc I vac them in a larger bag so that I can take out what I need then re-seal.