I put mine outside for two reasons:

1) Quieter.

2) Even though the bags collect most of the dust, they do leak some.
Therefore I put the DC in a shed just outside the garage so that the
extra-fine, extra-harmful dust goes outside.

The downside to having it outside is that I have to go outside to turn
it on or off (I know, easily fixed), and that it does suck some of the
warmer garage air out. Small price to pay for much less dust in the
garage.