When you arrive in Spain it is important to know some of the basics that are expected, especially if you are planning to be here on a permanant basis. It is true there are a lot of uncertainty with regards to the Resedencia Card and who needs it and when.
In short if you plan to live in Spain you need to register as a resident. The law gives you 3 months from arrival to do it, so if you haven't already it is a legal requirement that could end up with you getting in all sorts of proeblems further down the line.
A full run down of Frequesntly Asked Questions can be found on the Healthcareinspain.eu website. They answer everything from who needs it, when and why. Read more here.