Many homeowners having home energy audits are surprised to see that the exterior corners of rooms are much cooler than the rest of the walls. This is partially accounted for by the fact that wood serves as a poor insulator, but is often made worse by the fact that the framing lumber in corners (where several studs are nailed together to form the corner) is full of air leaks.
Standard practice in framing doesn't include air sealing those studs -- it's not generally seen as a particularly important job, and few would find fault with a contractor for leaving them unsealed. However, knowing the benefits of air sealing, I've made it standard practice to seal these corners whenever working with new construction. It's half a simple case of going the extra mile, and half a case of most contractors simply not knowing about the huge benefit -- most contractors are primarily concerned with getting the building up as quickly and cheaply as possible. My energy efficiency training has made me aware of the benefit of small steps like these, which can often have a significant payback for the homeowner in the long run.
It's a fact, but also an appropriate metaphor: If you decide to work with my company on your next project, I can personally guarantee that there will be no "cutting corners."