Why leave stored fault codes?
 

Ran a quick scan on my CDI with Xentry. There are no current faults (F) but there are lots of stored fault codes (f). What is the purpose of leaving stored codes in place? Just to document the history?

Stored fault codes can help tell the tale of what's going on. Sometimes you can get a hard fault that triggers a CEL but there can be other issues that contributed to the fault but aren't presented as a cause of the CEL. A good technician can breeze through what's stored and determine if anything else is relevant or just overly-verbose logging. This applies to most vehicles that store fault codes btw, not just Mercedes.

I was going to clear to get a "clean slate." Sounds like it would be wise to leave them?

Why bother? The code is generated by the computer or ecu. It has software bugs like any software does. Some soft code needs to be triggered 2 or 3 times to become hard code to turn on the CEL light. Hardware may have glitches. So just leave it and don't pay any attention. I would only clear it if CEL is on, read the code first. If the same code is triggered again then you have a problem.

I would print (or save as PDF) a baseline of what's there now, clear everything, then keep an eye on it. That way you'll know what has come back and needs to be investigated for intermittent faults.

Remember, don't put the computer on a network, either use a USB printer or a free PDF creator utility, then move the file out on a thumb drive to print elsewhere.

Getting a modern printer to work on a non-networked computer is going to be a challenge. First there's the challenge of finding XP drivers for newer printers. Also most driver installs make you go back to the internet and can't be loaded standalone.