Scotch bowls were hung over a fire to cook scotch broth* or porridge; both dishes need to be stirred constantly, hence the rounded bottom and no lid.
*Scotch broth is a thick soup containing barley, lamb, carrots, turnips, leeks, and cabbage. The recipe originated in Scotland, of course.
If you're lucky enough to get one, you can use it for food prep, or on the stovetop as a wok or soup pot, or as a serving bowl.
You could even use it in the oven for something. Use your imagination.
There's a video demonstration of cooking stir fry in a scotch bowl here.
Now, if you don't have one, you can still make scotch broth in a cast iron pot. When I decide to make some, I'll post the recipe.