When it come to draw the secret weapon when in need, you want it to be available and ready fast - the post-it note. It's a good idea to have them in a dispenser so it's takes less than a second to have one ready.
Sticky notes are one of the secrets of visual pathways, I use them to remind me to take thing out of the fridge before I go to work, I lave messages to my lovely wife such as "the news paper in the drawer" or when I'm on the phone and need to follow up with some questions I don't want to remember.
When you put them on the table and write with one hand they don't move around which makes it easy to use them while holding the phone on the other hand. than you can stick them, place them collect them or bind them together to a pile.
Taking a sticky note out of the dispenser is much faster than launching an app on your computer or smartphone.