Others already answered with information that you usually have more devices then just 1. So you can have access to your data from PC, laptop and your phone. I for once also like to have my own data my own. I.e. I have:

- my own email server

- my own files sharing service

- service for cardDav, CalDav etc.

- service for editing my own office files on mobile

- notes that are synchronized

- streaming of movies and music

- build and git server

- my own smart home service

- notification service

- chat

- VPN

- desktop sharing service

- my own DNS for blocking adds

- and others