Don't get lost in all of the detail.
The autocomplete attribute set to “off” can prevent specific fields from being auto-filled. For example, a form might ask for a pet’s name. In this case, it's likely that the browser will auto-fill incorrectly and cause problems (hence a valid reason to turn it off in this instance).
I want to bullet point some important points for you to take away from this attribute.
Values include “on” and “off”
Default is “on”
Possibly useful for extra security on password fields
The source of the suggested values is generally up to the browser
In most modern browsers, setting autocomplete to "off" will not prevent the browers own password manager from asking the user if they would like to save their username and password information