How are linux versions different?

Question

linux

For example, what is the difference between Debian 7 and 8. In what cases does it make sense to update the Server software and in which it is better to leave the previous version. For example, the MongoDB page does not mention installation for version 8 https://docs.mongodb.org/manual/installation/ does this mean that it is worth the wait?
Vulnerabilities? As far as I understand, they are usually in the software and not in the OS.

Answer 1

It makes sense to read about the differences on the distribution page. There can be significant differences - for example, in CentOS 7 systemd, and in CentOS 6 - sysV init. The package base is different and sometimes very different. All must be read.

Answer 2

Versions of Linux distributions practically do not differ, except perhaps only in the package base.
It makes sense to update the Server software only if security updates have been released and the current version lacks the required functionality; in all other cases, it is recommended to leave the current version.
As for installing MongoDB on Debian 8, if not mentioned, then we set it as the old one (the instructions may not be even 200 years old), otherwise follow the instructions.
> Why is the OS not related to the software in your opinion?