To be clear, there are two relevant functions here:
- A user may choose to hide their Profile Stats page from others. This is done under Settings on the Profile Stats page and does exactly that. It does *not* affect whether information about your finds are visible on the rest of the site (top lists, challenge checkers, etc). If you have found the most caches in your country, you will still be listed at the top of that list, and so on.
- A user may opt out from Project-GC entirely (using the link provided by Jakuje in the previous comment). That means that not only is your Profile Stats not visible, but your name won't show up on any other pages. There will be an entry showing that there is a person with so and so many finds (or whatever the page is about) but there will be no name listed. Thus, others will know that someone else has more finds than they do, but they won't know who this person is. Opting out from Project-GC also means what it sounds like. Once you have done that, you can't use any of the features of the site except to opt back in.