For once I think a car analogy is actually useful. But, in this analogy, "taking all your valuables out of the car" would be like removing all the important documents from the computer. Which would be a reasonable thing to do, I guess, if the computer shop really needed access to do the repairs that they need to do.

Another possibility -- maybe the computer is so borked that you can't even log on to remove your important documents. This seems more like calling somebody because your key broke in the lock... which... I guess most people would stick around? It is a little bit of a mismatch, because it is a quick fix and it isn't like you can go anywhere anyway.

Also, people from the general public don't know how to write random bits to a drive. Deleting files doesn't actually wipe the information, it just marks the space as available on the OS. Repair agents could still take an image of the drive and recover many of those secret documents.

It should be standard procedure in the repair world to hand the hard drive to the user to take home and keep only the PC for servicing.

Be aware that this can be completely different between HDDs ("spinning rust") and SSDs. HDDs don't get data cleared until it's explicitly overwritten, SSDs with OSes that support TRIM shouldn't have a lot of stray data left behind.

Also when wiping SSDs get something like Parted Magic (since at least 2018 likely earlier) that can properly erase SSDs. DBAN is NOT appropriate for SSDs in any way - extra wear from the writes, and wear leveling means you have zero idea where they're actually going.

Well, the protection strategy for my valuables is not "leave the car locked in the shop". And then there's that one customer who's "rattle" is something in the glove compartment, to extend the metaphor further.

So, in keeping with my points above, I would probably move the really valuable stuff out, but for some customers taking everything out will prevent the technician from removing the issue (and they will probably be blamed for it) and if I feel the need to completely get everything saved out of the car beforehand, I would not trust that shop with my car, either.

Let's not water the analogy down so far that it loses all connections to the current case.

I doubt anyone would leave an album with their nude pictures in the car hoping that the mechanic wouldn't do anything with it. Like...posting it all over the block where the customer lives.