It's a common attempt to fix website weirdness.

Your browser keeps the files that make up websites around after you have viewed the website. The performance benefit from not constantly reloading the common elements is considerable.

Unfortunately, it's possible for something to get messed up in this cache, or it's possible for a file that was marked as not changing to change, causing the browser to use the now-incorrect saved copy. (Note that a shift-F5 on the page generally overcomes old pages in cache issues without dumping the whole cache.)

I have never run into a situation where clearing the cache fixed a problem that shift-F5 didn't. However, multiple times I have run into the related issue of old cookies that cause a modified website to barf. Removing the offending cookies let the website work properly again. (This has always involved persistent login information.)

I have also run into a situation where the presence of something in the temporary files on the computer would cause a program problems. The culprit was never identified and I know there was nothing the program was reading from the temporary files at that point--it was my own code. Of course it would never fail on anything other than a factory floor computer and saving a snapshot of the temp directory yielded no useful information. As they were factory floor machines it wasn't practical to simply set the offending machine aside for me to puzzle out what was going on.