A downhill (DH) bike is purpose-built for one thing: bombing down steep, rough terrain at speed. With maximum suspension travel and slack, confidence-inspiring geometry, these bikes eat up rock gardens, big drops, and jumps that would overwhelm other mountain bike categories. If you're spending most of your riding time at lift-served bike parks or downhill racing courses, a DH bike is exactly what you need.
The trade-off is that DH bikes are not designed for climbing. They're heavy, typically have only a single chainring up front, and the long-travel suspension bobs under pedaling effort. You won't be riding to the top under your own power — these bikes are meant for chairlift or shuttle access.
A DH bike makes sense if you're a regular bike park rider or getting into downhill racing. But if you only visit parks occasionally or want the option to pedal uphill, an enduro bike gives you far more versatility while still handling aggressive descents capably.