Innings eaters are a thread the needle type of pitcher. You have to get batters out, otherwise you won't consume many innings. If you get a lot of batters out while keeping runners off the bases, you're a mid-rotation mainstay. If runners are getting on base, you're not getting them out. Because pitching success varies from year to year for many guys, I don't find the definition very useful for thinking about roster construction. Like the concept of a fifth starter, a guy's an innings eater until he suddenly isn't - he improves into someone you want to feed innings to, or he gets worse and you want to minimize his innings, possibly all the way to zero.