What can Vagrant, Puppet, Docker, Chef do for a Web developer?

First of all let me say that I'm aware of related questions here in SO:

• Vagrant, Docker, Puppet, Chef
• Vagrant + puppet + docker
• chef-server - chef-solo - vagrant - puppet... which is correct for me?

Or articles out there:

• http://ift.tt/2maAJTu

But I'm having trouble understanding real benefit they provide for a web developer (e.g. Full stack developer with (PHP/react)). You know? None of them is that clear for me in:

• what facilities they could provide & how they make my job easier?
• When do they become semi vital for project success & non-self-repeating activities?

Would you mind clarifying these concepts/techs from my POV? and not just comparing/benchmarking them with routine "Vs." literature?