the can filter is for smell. if smell isn't an issue... why use it?

for me, my lights are cooled with one fan, and the air for the lights never contacts the growing area so it just goes out.

the can filter sits inside my flower room..

can filter > flange > can fan > 8' ducting > exterior wall > outside. mine hangs from the ceiling so as to get the warm air.

If your air source was shitty, you could certainly filter the air coming in as well..