On a EFI engine, not running an O2 senser will cause improper fuel setting, & timming setting. As the computer reading will be wrong!!This in turn can change running tempartures= damaged engine!!
I would add that I still run my o2 sensors and that I just hollowed the cats out. So that they are still in place just nothing inside. Never had a light come on and had better fuel and performance out of both. And yes the lights are still there and do work. I do still have an E-test done every year and have never failed that either