If you have more brain cells does it make your brain grow bigger and smarter?

During development : of the brain, about 1 1/2 times the number of neurons are formed than are found in the adult brain. The ones that are "extra", for a variety of reasons, are "pruned." There is an association between larger head/brain size & Autistic Spectrum Disorder. One theory is that normal " pruning" doesn't occur. So, having more brain cells may not be completely positive. Good question for you to work on!