Whatever you do, make a copy of the DAM Update Asset workflow and make changes to the copy if you're going to modify it. Then update the Workflow Launcher configuration to use your modified workflow.
As per best practices you should avoid directly modifying the OOTB workflow models.
It saves yourself pain while troubleshooting and avoids needless tickets in Daycare where one side A blames the product and the other side blames the changes to the workflow model and nobody in side A remembers changing the workflow model to begin with.
99.9% of the time workflow issues are on the implementer, and that rare 0.01% of the times it's usually some edge case with the product generally around some multi-dimensional layered asset that the renditions come out looking distorted or something.
What explanation to do you need for the workflow model? DAM Update Asset generally handles most asset upload use-cases. If you have specific file types you're trying to ingest you must modify the model and add in additional workflow steps to process RAW images, or use ImageMagick, use PDF Rasterizer. etc. This particular workflow model is transient so not much data is persisted around the workflow's execution history.
This workflow model is responsible for generating renditions of assets, creating thumbnails, extracting metadata / exif data from the asset, etc. Just look at each step they're generally pretty self explanatory.