As a Norwegian speaker, I often use "skulle (nok) (ha) gjort" if I am disappointed that I failed to get something done, and that it is now too late to do it, and regret my mistake. For instance, an action bound to a specific event. Now that this event has passed, it is too late to do it. I use "skulle gjøre" more about less serious things, such as chores, that I simply postponed, either due to a lack of time, or lack of motivation. Example: "I was going to do it, but didn't get so far yet". On the other hand, "skulle ha gjort det" = "I should've done it".