Design: in what detail should you document the commercial flows of a product or system you are learning?

I work on applications that have user documentation but is not organized or updated to the current version.

Is it worthwhile to create my own documentation with screenshots and notes on all the current business operations that can be done with the product?

I think this is useful because it formalizes the various procedures that the product performs in my mind. However, this obviously takes a lot of time and may be an exaggeration.