The eFG% is the percentage of three-point shots made. The reason it is different from field goal percentages is because it accounts for the fact that three-point shots are worth 50% more than two-point shots.
The formula is:
eFG% = (FGM + (0.5 x 3PTM)) / FGA
This formula benefits players because it gives them a greater shooting percentage. They deserve this higher percentage because the three-point shot is a lower percentage shot. In other words, less three point shots in comparison to two-point shots are scored. If the two-point field goal percentage is used for three-point shooters, they would have a lower shooting percentage.
For example, if a high school player makes 20 out of 40 three-pointers, the player would be considered a 50% shooter based on regular field goal percentages. By using the eFG% formula, the player has a 75% shooting percentage. This makes a substantial difference.