If you buy a stand alone app that version it is good for life and updates but if a new version comes alone
at a later time you would have to buy it again usually at a discounted price and save your install download for future installs.
Or you can buy a subscription like Object Desktop which has to renew each year and includes a lot more apps
and updates and new versions if your subscriptions stays up to date .
Check out OD here https://www.stardock.com/products/odnt/
Stardock Community Assistant