You’ve just finished working on a complex feature. A future engineer will need to improve upon or fix potential bugs in this feature.

Your project manager needs clarification on a certain edge case.

You've just landed a new job, your boss asks you to fix a bug in a legacy application  you know nothing about. You are now looking for non existent documentation :(

The product manager reports a bug, assigns it to you. You start to investigate what seemed like a small bug has not taken several hours to gain context. 

You are the only developer that understands the code base well enough to train others

A new developer asks for documentation on feature X. You then record multiple sessions to add context and training material.

Impress your boss with accurate understanding of the knowledge domain

Reduce knowledge loss between cross functional teams