On the Practice Ground
You can measure the exact distances you are hitting the ball on the practice ground by using a rangefinder. Getting accurate data like this will be of great benefit during subsequent rounds. Use it to get the true distance to any flags or greens on the range, or to other landmarks, and you will find out exactly how far you hit a certain club.
On the tee
You can use the rangefinder to check distances to fairway bunkers, to the far side of any dogleg or to other hazards. This helps you determine the correct club to play.
From the fairway
With a rangefinder, you can measure the exact distance to the pin. The early models sometimes had difficulty focusing in on something as narrow as the pin, but modern rangefinders have a pinseeker function, ensuring you get the distance to the pin, not to the tree behind it. You can also check your carry over bunkers or water in front of the green.
Speed of Play
Using the rangefinder can speed up your round considerably. Once you are accustomed to using it, it only takes a few seconds to use the rangefinder to check your distances. This is much quicker than searching the fairways for distances on sprinkler heads, or trying to work out the distances in your yardage book.