Originally Posted by
Maelochs
I'd say that riding outside is generally a lot more enjoyable (based entirely on personal preferences) and it takes a lot more effort---everything from wind resistance to inclines (however slight) to the constant motion and adjustment the rider has to make---which we all do pretty much unconsciously) which all adds up to a lot more going on.
I haven't used a trainer for years, but they do have their advantages. You don't have to hold anything back, you can totally control how you structure your workout, you don't have to carry junk, virtually nonexistent mechanicals are easy to deal with, riding conditions are always comfortable, etc.