I don't know all of the advantages, but here are some things I've noticed.
1. There's a "My Wallets" tab where you can see all your funds in one place. GDAX didn't have this.
2. The deposit and withdrawl process seems simpler
3. I personally prefer the look and color, it seems sleeker...IMHO
Other than that, I didn't notice much difference. I think Coinbase mainly did this because they have more brand awareness now and they want to bring GDAX back under the Coinbase label.