I’m not sure how to fit tagging/parenting into my workflow.
For example, I write a quote. Should that card have a parent of Quotes? Or should it be tagged #quote?
Or, I am writing about my personal growth. Should all cards be tagged #personal-growth, or should they all have the parent of Personal Growth? Or both?
EDIT: I guess that this question ties in with my other one here about what to do with my “Thoughts”.
If every card has a parent AND a tag, then it won’t be a Thought but a more coherent piece of knowledge??
Today I created a card entitled “Two favourite photos from today”. I have tagged it #photography. Should I also give it a parent of “Photography”?
Welcome here @dmsharpe
I usually use the parent/child relationship to build hierarchies, like folders on a computer. Supernotes allows a card to belong to several ‘folders’, and that’s very practical.
Tags help me to add more details, and to create sets that are transversal to the folders.
For example, you could have a folder, i.e. a parent, called ‘Books’ and another called ‘Movies’, and in both you could have cards tagged ‘Quotes’.
You could also have a ‘Work’ folder and a ‘Travel’ folder and have cards tagged ‘Photography’ in both, and tag some of them ‘Favourite’ (or use the like function for that).
These are just a few ideas, the possibilities are endless 
Thanks. Should every card have a parent? If it doesn’t, should I remove it from the outline to keep things tidy?
Should every card have a parent?
Not all cards need to have a parent, but in many cases it helps to keep things organised. To save your photographs you could, for example, just create ‘loose’ cards and tag them, without placing them in a parent/child hierarchy. They’d all be visible in the ‘Images’ collection, and could be found just by looking at tags, dates, etc. So it’s perfectly possible not to assign a parent to your cards.
should I remove it from the outline to keep things tidy?
If I remember correctly, the default card visibility setting is ‘Priority’, which means that all the new cards appear in the outline… and I personally don’t find this practical (except at the beginning when it helps you not to ‘lose’ your cards). So in the application settings, in the behavior section, I changed the ‘New card visibility’ parameter to ‘Visible’.