There are a lot of default passwords out there in the world. You can use them to get free wifi, but the bad guys can use them too.
Routers, Internet of Things devices, and web applications are common victims of default passwords. If you have the ability to change the password, change the password. If you don't change the defaults, you are begging to get added to a botnet, or worse.
If you ever install an application and it has a default password, change that shit.
Here's a useful list of default passwords for routers, in case you're into that sort of thing: https://www.softwaretestinghelp.com/default-router-username-and-password-list
Similarly, if you have a printer or an IOT device around, google the brand/model and "default password", see if anything comes up.