Potential Issues Upgrading? from 3.21 :O

I run Ubuntu 18.04 LTS and I installed calibre from the repository. When things work, I'm the kind of person who doesn't necessarily "upgrade" just for the sake of upgrading. Apparently the version in the repository is 3.21 :eek: while the latest version is 5.38! Wow...

So, my question(s) is(are) is there any real reason to "upgrade"? And 2) if I do decide to "upgrade" would there be any potential issues of which I should be aware "upgrading" from such an older version to the latest?

Thanks!