I work as a developer and I run many e-commerce websites. One thing I've noticed is that the shopping cart doesn't have the same behavior in different websites (whether it's mine or not). The main topic I'd like to discuss is the way we see what's in the shopping cart.
When we click/hover the cart button, display a dropdown showing what are the products we have and usually 2 buttons. "Go to cart" and "Checkout".
Show a side bar menu, similar to the menu. It's also similar to the dropdown option, because we stay on the same page but we can see our cart. This option however, show more products, since it goes from the top to the bottom of the page.
Direct link. When hovering the button, nothing happens, and when we click the button we go to the shopping cart page.
I don't know why these options are commonly used and what are the benefits of each. I imagine the 3º option is trying to make the user finish the purchase as soon as possible. Option 1 and 2 is more likely to buy more items, but less likely to finish the purchase.
The only problem I've noticed with option 1 is the consistency across devices. It's not optimal to show the dropdown on mobile.
But is it really bad to have a dropdown on desktop and link access on mobile? Is there anything I'm missing here?