Thank you, all your explanations make sense. I (sponsor) am thinking of providing a spousal "cover letter" only because we are married for a little over a year and no kids (yet) and primarily have evidence of financial interdependence and cohabitation, few photos with friends and family, and zero social media presence as a couple. Hence the thought of doing this. Thinking I'll do a letter stating how the purpose and intent of the spousal PR application is to allow our continued ongoing cohabitation and life together as a married couple (which if he doesn't get a PR will be limited to the closed work permit duration he is currently on), and that while he as the PA is adequately employed and therefore currently taking up bulk of the household's financial responsibilities, I'm contributing with long term savings/investments but I still am capable to support both of us financially should the need ever arise.
A year or more cohabitating and married is a rather straightforward case. Photos and social media presence are (in my opinion) secondary in nature, more important for those who have little history together.
That said, I don't know your personal situation, whether eg you have photos etc from marriage, if there are any cultural issues underlying (eg was the marriage arranged), etc. So use your best judgment.
My one suggestion is: take a couple weekend trips and get photos as a couple, ideally 'doing things.' Perhaps make the effort to invite some friends out for dinner or an event. Or add some photos of you doing things together - go bowling. Failing that, go to a local park.
Because overall I'd say those 'real evidence' things are more useful in support than the overall letter of explanation, and your time would be better spent obtaining actual evidence.
Oh - 'purpose and intent ... is to allow our continued life as a married couple' - that's so obvious I see very little (zero) need to explain that further. Of course the point of a spousal app is to allow the spouses to live together on a permanent basis. That's exactly the kind of filler and blah-blah content that their eyes will glaze over at. Facts, actual evidence are way better. Romantic novels at the last resort.