If you are new to DMing, or looking for inspiration to create your own worlds and adventures, I'd say its pretty essential.
If you're an experienced DM and you're running an existing campaign setting (published or your own), or existing modules, it's more hobby reading material (optional).
Probably the only 'must have' content in it are magic items and *maybe* some of the wilderness travel stuff/downtime stuff. Even then you probably don't need those if you're running say Tyranny of Dragons.
If you're an experienced DM and you're running an existing campaign setting (published or your own), or existing modules, it's more hobby reading material (optional).
Probably the only 'must have' content in it are magic items and *maybe* some of the wilderness travel stuff/downtime stuff. Even then you probably don't need those if you're running say Tyranny of Dragons.