Why should I inherit a interface instead of inheriting its contract in solidity?

Question

I'm learning the usage of interface in solidity, and I think its most usage is to provide a API for other contract or Dapp to call.

I also notice a lot of contract inherit the interface. I wonder what is the advantage for a contract to inherit the interface of another contract instead of inheriting the another contract itself?

I can't convince myself since the following reasons:

1. Inheriting interface needs to write the interface first.
2. Inheriting interface needs to rewrite the function code.