If you have the space (eg: hole in the sink deck) to mount the airgap, I *strongly * recommend you put one in.
If your sink drain backs up, the gap will prevent the dishwasher from resembling a septic tank and filling up with sewage. Ive seen dishwashers fill up with sewage / drain water so badly that the muck poured out onto the floor when someone opened the door in a situation where the drain backed up and the sink was filled almost completely with water.
Also, IIRC, airgaps are called for in the uniform building code, which is a national reference - not all areas adhere fully to it, and some will go above and beyond UBC in their requirements, but it’s a good starting point.
For the definitive answer, check with your local building/plumbing inspector’s office.