What is special about carpet cutters?
Carpet edgers are designed to trim a carpet to the right fit against a wall and under baseboard trim by sliding along the trim. 

If you're referring to the basic utility knife, they're designed with an appropriate angle to reduce hand fatigue, but any utility knife will do fine.

A typical scissor won't have the leverage needed to shear the very heavy backing fabric (jute) that  carpet is built upon. Specialty shears may, but they'll be slow and are only suitable for small fitment work.