It's a different feel. Some prefer it. A two-stage rifle trigger feels like a 1911 trigger -- first you have some slack, then the takeup with very little movement, then the break and little overtravel. Many rifle competitors (e.g., CMP, service rifle) use two-stage triggers.
The stock AR15 trigger is usually 6+ lbs and can't be easily, reliably, and durably improved without replacement.