so i actually read beyond the TLDR and the reasons are:

- it gets attached early so fully cached, even if later cache is busted

- it gets included in every request automatically, so if your following requests are going to keep triggering File Read requests it will be much cheaper and faster to keep sending it

My main question is how this works if Claude itself keeps editing the file. Surely then you are sabotaging your own cache rather than helping it.

The things to add this way would be static files that you don't expect to change and to be highly relevant to the following requests. Especially if you want them to be mandatory reading and not just hope the agent will read it.