For example, you have 'Products' folder with urlalias 'products' under 'Home' folder (look at default ezwebin's installation result). Now set you 'PathPrefix' to 'products' (site.ini, [SiteAccessSettings] section):
PathPrefix=products

And then create another 'Products' folder as child of already existing 'Products' folder with the same indentifier 'products'. That child will have 'products/products' as urlalias.
So, by taking into account 'PathPrefix', you have to write something like the next into browser address input box:
http://yoursitename.domain/products
to get to sub-folder 'Products' which is published under root 'Products' folder.
But the result is that you will get the parent 'Products' folder instead.

The same is truly to all of sub-children of 'Products' folder.
For example 'http://yoursitename.domain/products/somenode' will try to get you to
'products/somenode' instead of 'products/products/somenode' in case of 'PathPrefix=products'.