So say you're in a village. Calming music playing. Then you leave said village. The music starts to ramp up, maybe adds more instruments. Then you're in combat, and the music starts playing faster and puts emphasis on the percussion instruments. Then you get to low health and need to lock in, and the music quiets down a bit, and integrates a heartbeat into the mix to add a sense of urgency. Then you die, and the music rips off with a static noise, followed by some kinda "you died/game over" jingle.
Adaptive music is awesome in literally everything, the only good reason for not having is budget constraints 😔