[jpsmith1cm]

out here where I work some stores run 1 compressor per suction group off of a VFD.

the benefit is capacity control you will be able to nearly match the exact load requirement. your energy savings is not going to come from the compressor on the VFD, but rather from the other compressors not on the VFD that will cycle less.

This is the correct answer.

Compressors are deemed a "constant torque" load. VFDs do not save energy on these. It still takes 'X' amount of force to turn the motor at 50% speed as it does at 100% speed.

Fans (both centrifugal and prop) are deemed "variable torque" loads. This is where you can see some very real energy savings by use of a VFD.