Power Consumption for Starter and Drives

As PWSlack so aptly put it, the energy consumption of a motor is always "automatic" in that the the motor only uses what the load demands, plus any efficiency losses. That is true with or without a drive on it.

Contrary to popular belief, the only way a drive saves energy is by eliminating some OTHER forms of losses in a VARIABLE process system; for example eliminating losses across a throttling valve in a variable flow pump system or air guide vanes in a variable air volume system. If the system is not variable, the drive will actually consume MORE energy than if the motor were run DOL and the losses in the process were dealt with elsewhere. So if you have that SPECIFIC situation, then replacing a drive with a starter might actually reduce losses. But in that case, someone had misapplied the drive. It happens, but before jumping tp that conclusion you must thoroughly investigate ALL possible operating conditions to see if there is something the original designer was counting on the drive to deal with.