Useful when you are searching for a new place to stay and you found that a listing you have already checked out is not for you. This way you can remove it from the map and only the new listings and the ones you are interested in will appear!
To exclude it you have to click a button:
Then the list of excluded listings will be in the local storage, which you can find in the developer console of your browser.
It will be under daft.ie local storage, with the name excludedListings.
You need to have Tampermonkey installed in your browser. Then you can install the script from Greasy Fork.
If the "exclude" button is not showing up, try reloading the map 2-3 times until the map zooms in and out briefly when it loads. Then you should see the buttons appear and the already excluded listings disappear.