Questions about "Restrict Background Data" on Galaxy S5

Hello all,

I have a Samsung Galaxy S5 on Verizon and I'm always looking for ways to improve battery life since I use so few features of the phone (call/text/camera, a weather widget, Gmail, Google Maps, that's about it).

In the Power saving mode settings, I see an option called "Restrict Background Data". I've Googled around and found some information but none of it recent so I wanted to ask a few questions.

1.) Does this apply only to mobile data or also wifi?
2.) What qualifies as background data? For example, I would assume calls/text do not but would my weather widget still update at its specified intervals and would Gmail tell me of any new emails?
3.) Will this affect my ability to get OS updates from Samsung and updates via Google Play?
4.) How much battery life does this actually save?