How to use the usb on a router?

[#1]

I am struggling to understand why routers have usb on them. I have seen it is something to do with file sharing, but how does it work and what benefits does it have?
Thanks
Mark

[#2]

Some people use it for network printers. Nowadays they are Wireless enabled printers though.
Some routers have USB ports so that you can put a 3G/4G dongle in them as a backup if your connection goes down for whatever reason.

[#3]

Also on some routers that support file sharing, you can put a USB memory stick or hard drive onto the USB port then the whole family can access and share things like photos and films.

[#4]

So if I put pictures and videos on the usb and plugged it in, how would others access the content if I am the only one with access to the router?
Thanks

[#5]

Other people on the same network as you could access the images / files.
If you don't share your network with anyone else then it would be a pointless exercise.

[#6]

Thanks for the answers