In modern versions of macOS, reinstalling macOS from Recovery simply "replaces the Core Operating System Files that allow macOS to startup correctly" directly from Apple's servers. This way, if such a file was damaged or attempted to be updated during a software update but didn't take exactly, the reinstall would pave over that with the latest version of macOS your hardware supports (and healthy versions of said files).
The only time your data is destroyed is if you erase your hard drive with disk utility before reinstalling macOS (on purpose), or if attempting a reinstall, your hard drive that holds your data failed (and as a result your reinstall failed), or if reinstalling caused your user account to be unexpectedly unlinked and or deleted despite the technology not intending to do so.
Avoiding data loss usually is as simple as doing a Time Machine backup first if possible. However, it's understood that most people would wish to consider reinstalling to resolve a startup issue (making doing a backup impossible).
Either way, you could consider taking it to a local Data Recovery specialist in your area to see about withdrawing files first if you'd rather not take any risks.
TL;DR - reinstalling doesn't delete anything. It just replaces/repairs the Core files required for the macOS to start up correctly again or whichever apps are included in macOS by default that you cannot delete (EG Safari, Mail, etc).