1Vegan, to answer the most important of your questions first, please do not ever worry about how many times you view the site, or re-visit a page. Do not ever worry about bandwidth consumption. While certainly considerate, it is absolutely not your responsibility so please do not ever feel this is the case.
Okay, regarding the cache files. Assuming you are using Windows, images and files are stored in a folder called temporary internet files. On some computers, there may or may also be a cache folder as well.
In Internet Explorer, go to:
Tools > Internet Options > General tab
There is a Settings button for temporary internet files. Click it. You will see somethng called "Check for newer versions of stored pages". Most folks will have it set as Every Time You Start Internet Explorer which means that every time you start IE and visit the site, it will check and update the files in your temporary Internet Files because the pages now contain new, updated content. This is normal and allows you view the latest posts.
Also under this same menu, there is a "slider" that lets you choose how much disk space to use for the temporary files. If this is set to a low setting, such as the case with the library, it is possible that the library computer has different files stored in the temp files folder because other peole have visited different sites. So when you use it, it replaces those files with the ones with VB
I hope this helps better explain the cache thing and, again, never ever worry about using bandwidth here. View as many of the threads and participate in as many as threads as you like.