pdzoch
Explorer
Grappling is great. It prevents the enemy from moving, which means for example that if you push him prone with another attack (or with Thunderous Smite, etc.), he can't get up and he's stuck making his attacks at disadvantage while you attack him at advantage. Even if you don't push him down, you can now spend your turns Dodging while the rest of the party kills him to death from range, which (provided you are smart enough to have a good AC that synergizes well with Dodging) makes grappling essentially equivalent to a kill, since he can't just ignore you and go attack another party member who is less well-defended.
Grappling also prevents an enemy from gaining any benefit from his own Dodge, since Dodging stops working if your speed drops to 0, and being grappled sets your speed to 0.
There are also occasionally opportunities to make the enemy pay in other ways with grapple. For example, if your party druid has cast Protection From Poison on you (1 hour, no concentration) you can now drag the enemy into a Stinking Cloud to deprive him of actions without much risk. A Tiefling might grapple and drag an enemy through a Wall of Fire, and a raging Barbarian might drag one over Spike Growth, and an Aarakocra or monk might drag an enemy off a cliff. Etc., etc.
I agree. Grappling is a technique to support the team. In a way, it is a debuff that the non-magic users can do to an enemy to enable the party to better affect the target. A good grappler can even force other conditions/effects on the target (move to another location). These are physical mechanics that several magic mechanics normal perform. (And since they are physical capabilities, they do not require a spell slot!)