Absolutely! As a guitarist, learning music theory will help all aspects of your playing; from creating exercises, to playing covers, to expanding creativity. Believe it or not, I have had guitar players tell me that they refuse to learn theory because it hinders their natural creativity. I suppose I can understand this logic. There is a certain creative advantage to just sitting down with your guitar and playing without thinking. But what happens after you come up with a cool riff or song idea. Chances are you involve yourself in a grueling trial and error approach to expanding on that riff or idea. This approach often leads to extreme frustration, not to mention it is horribly time consuming. This is where learning music theory becomes a huge advantage!
Just because you know some music theory doesn't mean you have to use it for everything you do. You can still sit down and play creatively without thinking about what you are doing. But armed with a bit of theory knowledge, you can now more easily expand upon that cool riff and turn it into an entire song. I often use this approach in my own song writing. I will sit down and mindlessly start cranking out riffs and lead lines until I find something that sounds cool. Then I will take the time to analyze what is going on musically: the key, the chords, the scales, etc. Once I have a general idea of what is going on, I can then use that knowledge to quickly expand upon the idea and come up with a vast quantity of usable material in half the time.
Another huge advantage to learning theory that should be obvious to all of you lead guitarists out there, is knowing how to intelligently construct a guitar solo. Sure, you can learn a few scale patterns and try to move them around the neck until you think you found what key the song is in, but that is very time consuming and often leads to dull and boring guitar solos. Not to mention you'd be completely lost and unprepared if the song changes key or uses a secondary chord function. Knowing theory allows you to thoroughly analyze what is going on with the chord progression you are soloing over and make deliberate and intelligent choices that will completely dictate the emotion of the song during your solo.
But what if you are just learning guitar to have fun playing cover songs? Music theory still provides a great advantage in this situation as well. Ask any seasoned guitar player that knows a little theory and they'll all tell you the same thing; having the ability to analyze a song musically will enable you to learn songs quicker, and greatly increase the efficiency of memorizing the song. It also allows you to have a bit of creative freedom with your interpretation of the songs you choose to play.
So if you still think music theory hinders creativity, I challenge you to research some of your favorite guitar players and try to find out their take on learning music theory. I can guarantee that the vast majority of professional guitarists know at least some theory and this is how they are able to develop their unique sounds and playing styles.
I am often asked by my students how long, and how often they should practice their guitar. The truth is that practice time will vary greatly among guitar students. Beginners will require more time to learn and interpret new information than intermediate players. Intermediate players will be able to physically play for longer periods of time without fatigue than beginners will be able to. And more often than not, life gets in the way and practice time gets cut short or all together skipped over.
Regardless of your level of guitar playing, their is one aspect of practice that remains constant...the length of your practice sessions is not nearly as important as the frequency of your practice sessions. Simply put, just 20 minutes of practice done every day can be more beneficial than 2 hours of practice done 3 times per week. The key lies in being able to positively identify your strengths and weaknesses. Once you know your strengths and weaknesses, you can use that information to set unique goals for each practice session. By narrowing down your practice session to 1 or 2 goals, you can actually be more productive in less time. You can use this strategy to create weekly or monthly cycles of practice sessions. Rather than trying to fit everything into one practice session everyday, spread everything out into shorter practice sessions throughout the week or even the month.
Finally, a word on how to handle your individual practice sessions. I like to divide my practice time into 3 categories; Warm-up, Needs Improvement, and Playing For Enjoyment. Since the length of practice session varies among guitar players, I advise my students to break the 3 categories into percentages. Your warm-up routine should be roughly 10% of your practice time, things that need improving should be roughly 50% of your practice time, and save the remaining 40% for enjoyment (after all, what is the point of all that practice if you can't enjoy playing guitar). Surely each category can be defined in many different ways depending on your specific goals for playing the guitar, but follow this general idea and your practice time productivity is sure to skyrocket.