I've also previously used that space for notification bars that hover over where your product would go (for errors, successful actions, etc.) So your product wouldn't fit on my site because that real estate is taken.
The main thing is finding something useful for this. This isn't a solution to anything, its just a piece of javascript. IMO having one of those floating around gets in the way of my user's experience.
Website owners typically have one important message or call to action that they would like each visitor to process. Since we don't have consistent design standards, the user has a inconsistent visual experience ingesting web content and messaging.
This happened with digital display ads. Services like The Deck have provided solid improvement with engagement through conformed ads in a single dosage per page.
We want to bring simplicity and consistency to the web experience. We hope that a thoughtful design, one well-crafted sentence and a call to action is what we need to increase engagement on your website.