Skip keywords that have been processed?

I noticed that there is an option for "skip keywords that have been processed", what does this option do and how does it work exactly?

It will keep in mind what search engine delivered results up to what page and will either skip that search completely if the last page was reached or will continue from the last known page from previous project run.

If you don't use this option, it will always use all selected search engines + keywords and start from page 1.