What happens if I turn off 'find my phone'?

My phone just made me have to re activate it, randomly. I have an iPhone 6. I barely remembered my password so I dunno even how I got back into my phone. Why did I have to re active my phone and how can I stop it from happening again? Is it because of the feature 'find my phone' and what happens if I turn that off?
I'm so bad with apple phones and I don't know why they make things so complicated.

If you disable it then you can't track your phone if it is lost or stolen. It also allows a thief to restore the device via iTunes so they can then use or sell it. Having find my iPhone enabled forces them to enter the password when attempting to restore it.