With amazon prime membership, there are many items that don't have shipping costs.
I like amazon grocery because there are some things there I just can never find in my local supermarkets. Sometimes, the prices ARE better.
I recently got some Indian soup that I have never seen on the shelf of a grocery store. Knowing the price of soup in general, it was a pretty good buy, although I couldn't compare it to anything.
The delivery is a convenient feature of online shopping.