In addition to the server and desktop clients, there are mobile apps for both Android and iOS.
Can be used to connect offsite server for backups or hosting but seen as part of your local network. No need for open ports on your home router.
Easy way to access you Plex servee when away from home.
Storing a hard disk in a car or any other moving vehicle is highly not recommended. The vibration will kill your drive. There are stories of companies moving drives on trolleys across their carpark to find the data has been lost.