In the end you have to know what you are doing, but it will point you to very useful tips and show some warnings that you can look to improve the security of you server. But in this, I still don't know two SysAdmins that concur on the best way to harden a server. There is a lot of things to consider and there are very strong opinions on how to do certain things.

But without doubt, it's a very useful tool, even if you know what you are doing you can use it like a checklist to know if you are forgetting something. It's not perfect (nothing is, and less in this field) but I can only recommend it.