Gahaz Bandit's is an intermediate grind-zone. Gahaz mobs are primarily fought for quest-related reasons and also used as a grind spot early on. The xp here is decent but nothing special. With that being said, this spot is decent early on, but you should focus on questing until you reach level 56 - once level 56, you can grind Polly's for better, more profitable rewards. Polly's is also one of the best spots in the game for xp. If you reach level 56 but still cant kill pollys Crescent mobs will do until then.
Gahaz is located North of Sand Grain in the desert; The desert is located North of Altinova, the fourth major city in Black Desert.