VPN's can also be used for other things such as accessing websites that cannot be shown throgh surface web (The display in which the internet is used by most people)
A common misconseption is that the dark web and the deep web are the same thing. They are not. The deep web contains things like secret government files, financial records, and legal documents. The dark web contains things such as illegal drugs, red rooms (very rare), the sale of illegal firearms, and human trafficking (mostly from Meso America and Libya).
Even though you dont neeed a VPN to just surf the deep and dark web, not using one can put you in legal trouble. A VPN is mostly needed when using the dark web due to the content displayed there