I still do this. I keep a pocket sized card folio and a pen on me at all times. I go on daily walks and take my cards with me. Ideas pop up and I write them down on a card. Once a note is recorded, I insert its card into the back of my folio. Once per week (at least, on a schedule) I empty the folio of ideas and enter them into a my digital notes system (bespoke, made with emacs). From there I can label, associate, file-away, and prioritize different ideas.

I find the main benefit to doing all of this is the ritual itself. By revisiting ideas a couple of times throughout the "card lifecycle", I form associations between disparate thoughts.

For maybe 20% (idk) of the ideas I jot down a smartphone wouldn't have been as easy or as useful. Besides, I like to go on walks without a phone - when I go to record a idea I am guaranteed not to be distracted by some notification or prompt from the rest of life.

If you can stand to look like a throwback or hipster or wackadoodle, I recommend keeping a small note pad or set of cards on you all the time.

another use, less relevant in today's world than in the world of a few years ago: When meeting people at a coffee shop or restaurant, it was nice to hand everybody a card and a pen and ask them to doodle something. This was a nice icebreaker.