Ventilation is definitely a concern. Some closets don't have good access to ventilation without drilling holes, etc. A lot of closets are located in the interior of a room as opposed to being against an outside wall or near a window. Also, depending on the size of the closet it could become more difficult to access your plants as they grow bigger. I can attest to that as watering has become an adventure for me as my two plants are seriously crowding my closet. With a grow tent you can pretty much put it where you want (like close to a window or an electrical outlet). Plus most grow tents have holes already for ventilation and bars to hang filters and/or fans. It's obviously more expensive to purchase a nice grow tent than it is a closet, but depending on your circumstances a grow tent could potentially work better.