Hey there, I'm more of a newbie to cycling than you are but have experience training in other sports before. I'd say that following a specific program helps you get the most out of your time on the trainer, and it's what I do in my hours on the turbo. You can work on, say, sprints in one session, strength in another and pedaling economy in a different one - changing it up keeps you focused and keeps the boredom at bay!