Here's an example. I redid Anna Lynn's boots today. I'm going to sculpt them to look like the fancy boots in the concept drawings.
While improving the shape of the boots, these came in really handy. I'm sure you can tell why! By being able to see the feet inside the boots, it was easier to understand how the boots should be contoured.
And here's the concept turnaround of Anna Lynn's outfit, showing the look I'm going for with the boots.