Inside/outside your cover HAS to be kept on
Intake (sucking air into tent from filter the sleeve stops any dust and so on blocking the charcoal and helps perserve good air flow. (Also, if it gets really dusty, quick wash, not 100% needed, but extra clean airflow can only be good)
If you're using it as a negative seal. (Same applies. You'll see a build up of yellow dust, real grimy, also, with exhaust "filter inside tent" the sleeve will stop any excess moisture and clogging up ur charcoal with mold and such.
So, all in all. Keep in on.