When you're "retired" and coming back every month or two on a consistent basis and taking up 15 minutes of tv time, or constantly inserting yourself into the main event, you're holding back younger talent.
Bret "shoestring hair hobo" hart, Mick Foley and Ric Flair need to make their appearances less frequent. i have all the respect in the world for their careers, but stop coming back every other month.
It comes with age. Hart only comes back when they actually have a use for him. Flair hasn't been around for how long? Retiring doesn't mean they can't come back. Nostalgia, ratings bumps, and interacting with the stars of today are all perfectly good reasons for them to come around.