This depends upon various factors like your plants, the grow lights that you use, and your height. You can get away with a shorter grow tent if you are using LED or CFL grow lights However if you are using the MH or HPS grow lights then you can not place them closer to the plant canopy and have to keep the lights at a greater height from the plants. For this, you will need a heightened or taller grow tent. Some plants grow taller and want to expand so they need more space so if this is your issue you should go on for the grow tent to have more height and space for your plants to grow well.