The answer to that is “obviously”. If you are into playing real instruments than trying out GarageBand will only enhance the experience of creating new music pieces of your own. Even though it is not a requirement to learn GarageBand if you are a Musician. Still, the addition of GarageBand to your Music life will only make the experience great. Thus, it holds a lot of worth when you learn GarageBand and play a real instrument at the same time.
To simply put it, there is just no harm in trying out this Music Editing application. If you are willing to record and produce some quality sound and music, then GarageBand will just be perfect for that job.
GarageBand is built not only by keeping professional music producers in mind but also those many beginners who are trying their hand with instruments as well as techs. It has a very smooth and user friendly interface which goes with largely anyone who knows their way around music and tech.
So simply putting it. There is just no harm in learning GarageBand if you are willing to go a step further in your music career.