> If I really wanted to add a decedent selector from a body class to .class1, I'd start a new nest on the body tag.

a) maybe you don't really know how far up the chain that tag gets called from.

b) it creates new selectors for class1 and class1.class2, as well as class1.class2's hover

c) creates a hyper specificity

now, I'm not advocating this usage of SASS - but it can be a handy hatchet when you need to support multiple themes with minimal changes/effort, much to the chagrin of specificity and maintainability