The benefit of doing this is three-fold. For one, you are more than likely not going to functionally know how to re-create some effects which will force you to go out and read targeted tutorials. Second, you will notice the subtleties of the design that you are unlikely to notice when just looking, which will help build your design intuition. Lastly, you won't waste time trying to come up with an idea and failing through the execution; you will start with something great and end with something (hopefully) great.
Clearly this isn't the way to learn the creative side of design, but it will build up your skill-set such that you will actually be able to execute when you have a vision.
For reasons beyond my comprehension, I opened Photoshop one day and everything just clicked, and has been ever since. I can't say for sure if it's from working with so many different designs or styles, or being exposed to them, or just recognizing the styles that I preferred, but it does happen eventually.
If you're intentionally trying to learn design and you put in the time to consciously recognize what you're looking at and how it works, I bet that light bulb moment would happen much quicker.