This page is asking you to confirm that you want to leave - data you have entered may not be saved.
I'm really glad that there is a warning pop up when you want to leave the article editor without saving the draft before that.
However, there is no warning when you fill in the data for new shows/actors. It happened to me a few times - I'd spend 15 minutes filling in the Cast details, my hand would accidentally move and I'd leave the tab - all gone! The warning pop up would prevent that.
I'm not sure if this needs to be in the support forum though.