Just depends on why you like to ride. About half of the time I head to Fiesta Island for a controlled, safe workout. Doing 6+ laps on a 4 mile track can get a bit monotonous. Still, when I head there I'm not thinking about riding for fun, I'm thinking about working out. I'm the kind of guy that likes to rep sets at the gym or swim laps at the pool or otherwise 'work out'. Does it offer a fun, recreational outlet? Maybe, in a sick kind of way
Other times I ride for recreation, particularly in the form of weekend group rides and mountain biking. Does it offer a training benefit? Of course.
There isn't a black and white line here dividing riding for pleasure and fitness. Personally I've become more safety-oriented over the years and see myself slowly shying away from road racing and training in general. The trainer offers a logical alternative. I know of a few older racers that stick to TT only and drive to Fiesta Island and do 100% of their riding there. They're fast.