Throughout my career, I have always made notes, mostly in a Moleskin or similar note book, a little are personal, but so much refers to my everyday activity as a Technologist.
A lot of these pages are scanned and saved to both Evernote, or more these days, Google Keep for easy search and retrieval.
So many notes are just a page in a book, looking for that one note or record of a conversation is mind numbingly difficult, but scanning into a pdf, and adding it to one of the above allows easy search and find, tagging and sharing.
I saw this detail on a roof to an old house, it was in need of repair, but before I could get a specification together I had to sort out the construction in my mind. What components needed to be replaced and what needed to be added to make the detail last.
Long range photos also helped to capture the detail, but drawing the detail helped to understand it.
Before drawing out any detail in CAD, I like to sit and think the detail through, what components are needed, and how they will fit together and in what sequence.
Will it keep the water out, will it survive
Another detail to the same room, this time working out the vally gutter before it was drawn up