They are very rare, and can dump a lot of snow if they make landfall. This one is currently dumping a lot of precipitation on the Outer Hebrides.
If this one doesn't die and tracks south it will pick up a lot of moisture off the sea and has the potential to produce a big snow event. It will also drag a lot of colder air with it, the models will need to play keep up now as its presence could alter this forecasted cold spell in a big way.
Saying all that they are very volatile systems and it could die out as quickly as it formed.