I wasn't properly diagnosed until I was 18 (I'm 19 now), but as a child I was suspected to have PDD-NOS, although I was never diagnosed with that. My mom had me go to a group therapy for making friends and social skills, I think. I don't think I paid any attention, or even tried to make progress in therapy. I honestly didn't even care about having social skills. All I cared about was that at the end of each session, I could pick out a "prize" like a small knick knack toy, sticker, that sort of thing. So, I did therapy on and off as a kid, but I didn't make any progress socially (that I know of). I was always the odd ball, and I still am, and I'm ok with that.
I think if I had an autism diagnosis earlier it might have helped me and my parents to deal with and prevent my meltdowns. I had frequent, and sometimes violent meltdowns as a child, and it was frustrating because I didn't have the maturity or vocabulary to ask for help, or to explain what I was feeling. This led to frustrations and sensory overload and meltdowns where I would throw things and hit myself and generally cause a ruckus.
I think it would have been very helpful, or at least easier, if I was diagnosed earlier in life.