Main benefit is the discount in listing fees, including listing upgrades.
Another benefit is that if you have a large inventory, you can sort them into category, which makes it easier to buyers to see what you are selling in your store.
Also, buyers can search within your store.
It is of course a benefit if you can make your store look really professional too.
In my opinion, it is only worth it if you are selling many many different items.
Also, you have to know if BIN or Auction listing works better for your item.
Hot or rare items do great with Auction listing and you incur the least listing fees starting with low auction price.
An eBay shop is useless for Auction listings.