From what I understand with the semi-chisel is that each of the cutters takes a smaller cut than compared to full chisel, but each of them equally cuts and this extends their ability to stay sharper longer. The full chisel takes bigger cuts (digs a little deeper) and so there is more stress on the cutters and they tend to dull quicker (compared to semi-chisel).
When I was selling chain, I would sell the person whatever they wanted, if they didn't know what they wanted, I lead them towards semi-chisel.