What is this beast? (JPBO wooden groove plane)

I have a wooden plane which I don't quite understand.  It has an arrow shaped iron and metal skate running down the middle.  Unlike most plows I've seen, the iron is not grooved on the back to fit into the skate.  There is no nicker so I assume this ain't a cross grain cutter.

It looks like it will cut a groove 12mm (1/2 inch) wide and deep.  What would this be useful for? 

The plane was made by JPBO in Denmark and has a Sheffield iron.

Thanks!

~ Derek