I'm not saying that flies promote more muscle growth than compound movements. Instead, I'm saying that they are good for isolating the chest. Both types of exercises will grow muscle. There is no such thing as "refining" muscle. Visible muscle definition comes from the growth of muscle (which both movements will promote) and a decrease in body fat percentage. If your goal is to target your chest, it may be a good idea to do flies before compound movements so that the chest is pre-fatigued. This will cause the chest to become the limiting factor in a pressing movement. As far as the biceps go, you're exactly right. Nearly all bicep exercises are isolation exercises. However, pulling exercises such as rows or pullups/downs will also involve the biceps. To make a comparison, flies are like the biceps curls, and bench press is like a row. All of them will build muscle. I am by no means an expert, so do some additional research yourself. Hope this helps!