Every time you're using multiple words as a single adjective, yes. For example, if I were to say that Joe Biden's treasonous pants-shitting-and-child-molesting ass has earned its place in the oven.

Yes (lexico.com)

My non-grammar-Nazi understanding is that it indicates what the words modify. It's like parenthesis for grouping in a mathematical expression. It clarifies that soon and to modify be, rather than wife.

My mom found her little used kitchen mixer. My mom found her little-used kitchen mixer.

In the first sentence, it seems that the kitchen mixer may be “used,” small, and old, but with the correct hyphenation, you can see that the mixer is actually “little-used” or perhaps, almost brand new.