Every single person with kids either wants this, or just doesn't know they want it. That is not a small market. Do you want your kid to have access to your email, saved credentials and saved payment cards? No.
You want it if you yourself use the iPad for more than just watching Netflix, and you ever hand your iPad to your child without locking them into a single app using that feature.
Otherwise, they can do things like delete incoming chat messages you haven't yet read, delete any/all notes/photos/ etc, and a hundred similar things — and in many cases, it's easy to do accidentally.
