LM uses the term "Booking Classes" for articles purchased. If you were to purchase stationary at the local bookshop, you might buy paper and pencils. These are clearly different articles, with different prices. Paper would be charged in grams, thicker paper and more sheets per stack would lead to a higher price. But how about pencils? Is a red pencil different from a black pencil? Yes to the user. No to the pricing system.
Let's take this example and apply it to sheep. Lamb1, Lamb2 and similar booking classes typically differ in weight and (possibly) fat. For LM there's no need to separate these booking classes. They're just "lambs" and will be prices according to the lamb grid. However, sucker lams (or new spring lambs) might be prices to a different grid. They hardly reach 10KG, which is where most grids typically start. So we encourage our users to rethink the way booking classes are used.