Tools for Composition and Improvisation
Music theory makes music beautiful in the same way that understanding that snowflakes are made of delicate unique structures makes snow beautiful.
Music theory isn't about how well you can read sheet music, but it makes reading music easier. It doesn't tell you what to do, but it lets you understand and communicate with other musicians. It also lets you sometimes see why certain musicians sound the way they do. Giving you a method for impersonating their sound and working it into your natural musical vocabulary.
Sometimes music theory gives you a great method for composing songs. Or a clever way of creating a musical puzzle for the heartiest of musicians.
Composing music doesn't always mean sitting down with a pen and hand writing each and every note on a staff for every instrument. It very frequently looks nothing like that.
Writing music can be a fun interactive process that goes from games to group activities like jamming!
There are a lot of compositional techniques that don't use a lot of music theory. The two aren't mutually inclusive.
Another thing I encourage that everyone learn but don't require is how to read sheet music without looking at your hands. It's an amazingly useful tool to have.
Improvisation, or making up music as you go, is composing on the spot. So if you have several ways of writing music, your ability to make up music will get better too!