That's more a question of what you've got it plugged into. If it's plugged into something that's already got a lot of clean gain, you probably don't NEED a preamp. If you're after a particular sound, getting a preamp that's tailored to produce that sound will help you get what you're after.
I'm sure you already know this, but it bears saying for anyone who reads this thread later on. The AT2020 comes in two versions: One has a USB plug and the other has an XLR. The USB variant can't use a preamp. It plugs directly into the USB port on a computer. The XLR variant can be plugged in through a preamp or not, but will still need to plug into an XLR input.
Getting back to your question, you can always try it on its own and hear how it sounds before dropping money on a preamp.