A capo can wonderfully boost your creativity on a guitar. It's simple and easy to use, even humble, and it raises the pitch on the guitar strings when you clamp it on, similar to putting the nut on a higher fret. You'll be able to get a song on a tricky sharp or flat key signature, or be able to transpose a song on a higher pitch while still using the exact same chord shapes. You can use it with an electric or an acoustic guitar.