Thanks Ken
I'm sure you've noticed that as a regular visitor to a website using XC SEO, that the url for a product often looks similar to this: whatever-c-4-p-1-pr-6.html
A url like that is passing the category id, the category page, and the product id. All X-Cart needs to function, is the product id, but the other values are passed as they determine how the breadcrumb will appear at the top of the page.
So XC SEO allows these extra parameters in the url, as it's normal X-Cart functionality. The problem, though, is that to a bot, that page would look like a duplicate content page, same goes for pages that have the -print- parameter (printable pages), and there are other examples I can't think of at the moment.
The "prevent bots" config item ensures that if a bot is detected, it will not see any urls with certain unneeded variables, such as -print-, ?js=n, the -c-5-p-1 bit in a product url, etc etc. Instead, it shows bots only urls that don't have those extra parameters. Additionally, if a bot tries to visit a url that a bot isn't allowed to see, they get 301 redirected to the "clean" url.
If you have other questions, let me know!
Cheers