This torso was made using the skeleton mould I constructed ages ago. I don't need anything more than the torso in this case, because it's going to be a Feejee mermaid. I love those things.
Using a mould really speeds up the formulaic process of making a skeleton, which I find tedious. Ribs, shoulder blades, vertebrae - been there, done that, yawn. I don't need to go through that process each and every time I want a wee skeleton for something, and I have a short attention span when it comes to things I do for fun. This is partly natural laziness and partly the fact that I spend eight hours of a typical work day programming with no breaks. Either way, using a mould frees up my time to do more interesting things, such as figuring out how to add fishy elements to a humanoid head.
If I made the skeleton without a mould, it'd take several hours. Making it with a mould takes just a few minutes, excluding drying time (which doesn't count because it is time I can spend doing something else).