How to create a bootable backup for your Hackintosh? And why would you want to create one?

I want to create a bootable backup for my Hackintosh just in case anything happens to it.

I want to know:

• What are the benefits of creating a bootable backup? Why would I want to create a bootable backup?
• How can I create a bootable backup? What do I need to create a bootable backup?
• Can I use an external hard drive as a bootable backup? Which I would then transfer to my main SSD?
• How much storage (GB) do I need for a bootable backup?