Performance worse when name plates are set to "when targeted"

This is a very confusing issue to me. I got to the Crystal Tower, and decided to take Name Plates down for better visibility, being a Dragoon. I set most plates to "when targeted" so that I would have the plates on some occasions. The next day after doing so, I noticed a performance decrease, but thought it was just a 24 man raid being usually taxing. Today during a very low FPS 8-man dungeon run, I decided to turn plates back on, and performance doubled. Frame rate was impossible to deal with until I turned plates back on. Now I'm afraid to limit how they're used.

My question is what the reason for this is. Is "when targeted" extra taxing and turning them off completely would provide better performance? I'm on a laptop with an AMD A10 processor if that helps.