I'm seeing increased growth and huge pumps in my legs. My legs are my weakest parts so I've been trying just about anything I can to bring them up. I've also used IGF on arms (biceps and triceps) and chest. It's one of the reasons my arms are as large as they are at my bodyweight.
The one time I used IGF on my legs previously was a few years ago. I reasoned that for the dosage I used in my arms, the legs needed a larger dosage since they are much larger muscles. I used 300mcg in each head of the quad so that's a total of 1,200mcg in each leg. (I don't suggest everyone else do this. This is just what worked for me.) In one day from doing that, there was enough growth that you could see the separation in my quads. Couldn't see anything before that. These days, I'm doing 100mcg on the outer head of the quads because they were lacking.
Most people use it on an area they feel is lagging behind.