The major benefit of using a laser engraver is the production time you save. Laser engraving is much faster than rotary so you can complete more work in the same amount of time. The laser also leaves a cleaner, crisper look to your engraving and is a much cleaner process overall.
Laser engraving is versatile in that you have many more options for materials that can be laser engraved. You can achieve much greater detail and use more detailed artwork than with rotary engraving. Your upfront investment may be larger, but the return can make up for that with the speed and amount of work you can produce with the laser.