What will this do to my iphone?

My iPhone 4S has been lagging lately, especially on YouTube and it hasn't at all in the past. It's not connection because we got fibreop less than a year ago and it's working fine. My friend told me to turn off documents and data in iCloud and that would fix the lag but I don't know what that means (I know how to do it), and I'm not sure what will be deleted or not saved. Can anyone help?

If you turn off documents on iCloud it won't delete anything it will just not sync whatever items u turn off in icloud, whether it is documents or contacts or what have you.