I am always tempted to open up a Mind Map when I tend to work on a Software Testing strategy. The free flow of thoughts while thinking about the functionality, as well as things like performance and security, makes a Mind Map as my first go-to to paint a test strategy, so to speak. But once the thoughts are solidified and a more structured representation is needed for discussion to get into a BDD conversation or a product planning meeting, the Excel type of organisation seems to be helpful. I found one such nice example in a Medium write-up by Robbie Falck.
The other option could be to directly write these considerations in a BDD examples file. There are pros and cons of doing this. While writing BDD examples directly lets us convert this into executable specifications, the layout of the examples is exhaustive compared to a cell in an Excel file. In a product discussion meeting, as a quick check or a reminder for the sake of time, it would be easy to refer to a cell to discuss something rather than the long-winding examples, which could sometimes run into pages and might need scrolling back and forth which could take time.
My approach has always been to not to restrict product planning discussions to just functional aspects of the product, but to include all aspects of the product like performance, security, accessibility, etc. This is true irrespective of I use an excel file or a BDD example file, or even a Mind Map. To me, it looks like from an organizing perspective, Excel file looks better as I could jot down the various aspects alongside the functionality and get them discussed right away.
From the user flow or user journey perspective, a Mind Map or an Excel sheet will be useful, because there could be layers or hierarchies that could be easily represented in them, which is not the case with BDD examples file, which is just a flat layout of examples.
Those are some considerations for picking a suitable format for your purpose while capturing product behavior during product planning sessions. If you have any comments/feedback about this, please let me know in the comments section.
If you need help in test strategy and approach during product planning, feel free to setup a free introduction consultation with me, and then we can take the discussion further. Happy Testing!