In order to understand the western grip in tennis, you should first be aware of the bevels on the racket. On the bottom of the tennis racket there is an octagon, and each side of the octagon is called a bevel. Tennis players position their hands on these bevels so they can switch their grip quickly during a match while maintaining their grip on the racket.
The western grip is when you put the heel of your hand, and the palm side of your index finger knuckle, on the fifth bevel.
Using this a western grip increases the topspin, or forward rotation, of the ball. This allows you to hit the ball aggressively and keep the ball in court.
Another benefit of the topspin that this grip provides is the increase in the height of bounces. This throws your opponent off because it keeps the ball away from their ideal striking zone.
Using the western grip will give you a hard time with switching grips in the middle of a match. You will have to rotate your hand a certain amount of degrees depending on what grip you switch to, which can be challenging if you are not an experienced player.
You will also have a hard time hitting balls that bounce very low. If the ball is hit low, you need to get underneath the ball so it goes over the net, and that can be challenging with this grip.