Fast boot

You need to understand what the options mean, but it is usually obvious with the name, and fully documented in man pages.

When looking at a bash init script, you also need to understand what the variables mean. You do this by looking at the code to find what it is doing. In systemd you look at the man page instead. But only the first time, because the same options are used in all unit files so it's easy to remember, while sysv init script always re-implement the same things in a different way so you need to read everything.