Premium Ecomony is MUCH better than economy plus (for example Y+ on UA or C+ on DL, both of which are regular coach seats with a few extra inches of legroom/recline and perhaps early boarding or a free drink). There's also a difference in how one is booked on connecting flights, i.e., Eurobusiness or coach on intraEU segments or domestic FC or coach (even if Y+/C+) in the USA.