how can a bandwidth is useful in a hosting?

bandwidth is very important because files that are loaded to or from servers uses internet bandwidth to push files along the network at various speeds.

Bandwidth is a bunch of wires or fibers connecting servers to a network. Depending on the grade of the wire it determines how much data is coming across the network where your web-site is hosted.

ISP’s can put a limitation on bandwidth at certain times during peak periods or charge you a flat fee per month for bandwidth usage.

You can load most files in your web site. This excludes, of course, banners and pop ups and specific documents and images which are supposed to be loaded from a central server.

Bandwidth bandits link to images and other files directly to some other server instead of putting them on their local server. There are various reasons as to why they do this but one reason is to get as much bandwidth as possible to show their links and images.