A rangefinder provides accurate distances to objects on the golf course but unless you know how far you hit each club then there is little benefit in having the greater accuracy. To get the most use out of a rangefinder it is advisable to accurately measure the average distance you hit a golf ball with each club in your bag, either by using the rangefinder on the practise ground (hit a number of shots with the same club and get the average distance of all the good shots) or if you don't have practise facilities that would allow measuring (like a public driving range) then measure the distance of your shots during each round of golf you play to build up the data.
Speed up play: By removing the need to accurately pace out distances from yard markers, plus club selection requires less thought.
Confidence: By removing doubt about distance and which club to choose you may feel more confident in your shot. The fewer uncertainties going through your head when taking a shot the better, and being able to know your average performance with a club you can feel confidant that you can reproduce it.
Decision Making: By using a rangefinder to measure the distance to different hazards on the course you can improve your decision making ability. If you can measure the distance needed to clear a fairway bunker you can plan accordingly whether it is worth the risk to attempt, similarly knowing distances can give you confidence in laying up closer to a hazard than you would normally do