Using ORP requires using a lower CYA level, which means the cell needs to run longer to produce enough chlorine, and so needs to be replaced more frequently. You also need a somewhat larger cell than you would otherwise need to be able to keep up with the increased chlorine demand. The difference isn't dramatic, but it is noticeable. You also need to replace the PH and ORP sensors about every two years, which is also a noticeable expense. If you have ORP turned off, you can simply not replace the ORP sensor, for some savings.
Depending on details of your pool that are difficult to evaluate in advance, the ORP automation may or may not work at all. If it does work, the only real advantage is when you have a large swim party. ORP automation can add the extra chlorine required by it's self, while percentage based automation requires manual intervention when the bather load is suddenly higher than usual.