Here are the differences between CamScanner Plus and premium account:
CamScanner Plus is a one-time purchase.
CamScanner premium account is paid monthly or yearly.

Plus version registrants will unlock features like at least 200MB Cloud Space, high resolution scan, no advertisements, no watermarks, cloud OCR (100 times per month), etc. The account status is "basic".
Premium users can enjoy ALL full version features and will get additionally 10GB Cloud space, more folders, ID card mode, Cloud-OCR, exporting texts from the whole document with several pages(OCR), collage images, auto upload etc. The account status is "premium".

You will find more details about the difference on https://www.camscanner.com/team/price.

The Paid app & Premium subscription are designed for different user groups. If you don’t need those features, feel free to enjoy all the paid app features as always.