Sure, playing Boggle is wonderfully fun, but you can also learn while playing Boggle. It's win win! No one can tell you that you're wasting your time playing Boggle when you could be doing something more constructive with your time. If they do, just let them know all the benefits you're getting with each round of Boggle play!
Boggle teaches you quick thinking. As you struggle to find just one more word as the Boggle timer runs out, your mind is getting that much better at focusing and being creative under pressure. This great Boggle skill applies to many aspects of life, from taking standardized tests to sounding intelligent in meetings at work to being quicker on your feet in social conversation. Quick at Boggle is also quick at life.
Playing Boggle also improves your ability to make connections and form associations. During Boggle play you do your utmost to figure out what "L" could possibly have to do with "Y" or "R." Furthermore, as the Boggle round progresses your mind goes up a level and then tries to figure out what "lyre" and "dye" have in common. And if you can form "flyer" or "pyre" in turn, you're showing the much needed Boggle skill of making connections and brainstorming.
In addition, Boggle increases your skill at word manipulation and forming longer words out of shorter words (and vice versa). This is basically the ability to see how words are constructed and understand the relationships among words. Playing Boggle will help you develop the ability to glean meaning of longer words based on the shorter words or prefixes/suffixes within. Boggle can help you prepare for standardized vocabulary tests, advanced reading, or just the ability to interact with the intellectual world. And Boggle's a lot of fun to boot!