There are 3 good reasons to take a practice test early in your studies:
1. The test will give you a good taste of what you'll be preparing for over the coming weeks/months.
2. This will likely be your worst test score, and as your subsequent practice test scores improve, your confidence will undoubtedly increase as wel.
3. The results of this test will help you gauge the amount of work required to reach your target score.
If you're interested, I recently wrote an article for BTG about the importance of taking a practice test at the start of your GMAT prep:
https://www.beatthegmat.com/mba/2013/05/ ... st-already
Cheers,
Brent