Yes. I think Andy writes about this in several places.
Like in Getting Started in the README.
The three main difference to
Dictare that it preserves the order of elements, it iterates much faster, and it iterates values rather than key-value pairs.
His JuliaCon talk is very clear.
If you do a lot of insertion and deletion and not much iterating over keys and values, then Dict might be faster. If you do a lot of iterating, and not so much insertion and deletion, then Dictionary