It would only mean you could not run redis and mysql on the same host, and your default assumption about what port to connect to might be wrong 50% of the time.

It would only mean you could not run redis and mysql on the same host, and your default assumption about what port to connect to might be wrong 50% of the time. Easily handled, though. There are certainly cases of different software using the same unprivileged ports by default. It's probably more rare for the privileged ports.