To be sure the kid won't accidentally/purposefully:

- factory reset the device

- delete all your emails

- dismiss a (very important notification/message)

- spend $$$k on micro transactions

- change a random setting you never knew existed and don't realise why things suddenly stopped working

(I'm thinking here of young kids below the "understand the technology/responsibility well" age, possibly not able to read yet)

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.