the previous poster is right, but i think of it like this (and its just my opinion based on my experience and simplified to get across what i want to say).
I find that playing a TIE at enthusiasm 9/10 could give a similar team performance to playing a normal at enthusiasm 5.
Playing a normal at enthusiasm 9/10 could be similar to playing a CT at enthusiasm 5.
Of course to build up your enthusiasm you have to play TIE a few times
I dont know what a TIE at 5 enthusiasm is - perhaps a bit like a normal at enthusiasm 3 or 4?
and a CT at enthusiasm 5 is perhaps like a normal at 8 or 9 enthusiasm.
But if you CT at 5 enthusiasm bear in mind your following games will be TIE/Normal/CT at enthusiasm 2 or 3 which would be really bad compared to anything you do at enthusiasm 5!
hope i havent confused you (and the rest of the world) but believe me when i say enthusiasm management is very important and can be very effective when used properly. As is gameshape and tactical choice - all these things can turn an ordinary team into a great team in your league over the course of a season.