Half the time I'm filling up a measuring cup, I'm doing so at an angle, which means I need to stop and straighten it out in order to see exactly which line the contents go up to. Angled measuring cups mean I don't have to.
Amazon has a set of three, from OXO, for $US20, but if you shop around you might be able to get them cheaper, or one at a time. These may only save you a few seconds each measure, but what if you were measuring a lot of things all day? What if you were Walter White? What then? Exactly.