How easy is 'easy'?

I know that most people don't go hard enough on their 'hard' workouts and don't go easy enough on their 'easy' (Z1/Z2) workouts. I know that during a Z1/Z2 session you should be able to converse, breath comfortably etc and I try to aim for this. But when I look at my stats I find that I never do a workout with an Intensity Factor of less than 60%. Today I did a workout with an IF of 50% just to see how it felt. It felt incredibly easy BUT I enjoyed it and feel that I can comfortably train again tomorrow. Would like Scott to drill in to 'easy' workouts and let us know whether they can ever be TOO easy!