Isn't the whole point of running your own servers for mail/calendar/contacts/etc. that you don't have to rely on synchronising things via anyone else's infrastr

Isn't the whole point of running your own servers for mail/calendar/contacts/etc. that you don't have to rely on synchronising things via anyone else's infrastructure? I want to have multiple devices able to access my important data. I have no interest in sharing that data with Google, Apple, Facebook, LinkedIn, or $SMALL_TIME_APP_DEVELOPER and will actively avoid any system that requires me to do so.