It stops Comcast selling your topping preferences to other pizzerias

It stops a man-in-the-middle attacker from trying to exploit your browser/extensions/password manager by injecting code into that site (once the cert is pinned).

It might also help with SEO? Google's been pushing for https everywhere.

encryption works much better when it's setup without discrimination. I mean not the encryption itself; in the end, it's a tool not the aim.