They allow water and debris to move away from the ball's point of contact to provide cleaner contact with better control. Striking a ball from the rough can be unpredictable when there is a lot of debris between your club and the ball. Grooves help tremendously to make these shots more predictable.

Do grooves matter?

Clean grooves are critical as it reduces the chance of fliers. While a flier 7-iron might impress your mates, it will probably leave you with a nasty chip to try and save par. Research shows that you can lose up to 1,300 RPM of spin if you don't keep your grooves clean.

Why do drivers have grooves?

The only reason for grooves on the face of a driver is that this it is “traditional." In some cases it helps visually align the club head. The effect on spin is minimal and if anything grooves on a driver may reduce the spin rather than increase the spin.