Locking bundles is really usefull because it gives you the 100% sureness that you are the owner of the customization and no one changed it on the client's side. And you will never face a single issue if you work with DEV -> Deploy -> PROD (or SBOX) environments chain. I'm doing this since 10 years almost and I never experienced an issue. Of course this works if you are an SDN partner and you are building cross clients' bundles.