In my perspective, Stencil helps both designers and non-designers to prototype ideas faster. It removes the pressure of drawing repeated UI elements again and again.
In the case of a design workshop, stencil will help the team to try out more ideas. It helps everyone to scribe interface ideas fast on paper. And save your time for better thinking and trying out more possibilities. Even for Designer the story is same. And I think this stencil is a good item to have in any designers inventory.