Hashing it on the client side will make the hash the password. So the stored hash can be used as password by turning off the client side hashing, for instance by turning off javascript. You use https to avoid sending the password in cleartext over the network

I've certainly never encountered a web app that hashes locally before sending. I suppose it could work if this was at the account creation or password management stages, but you couldn't implement it at the login stage for obvious reasons.

I'm having trouble imagining what scenario client-side hashing would protect against.

Man in the middle attacks fetching for plaintext passwords

-- edit: using a KDF would improve it even more.

If the client only sends the hash to the server, a MitM also only needs to capture the hash.

Sure, but if they've MITM:ed your trusted certs, aren't you already boned in so many ways?