It’s just safer, makes it impossible for the chassis to be un-grounded while the machine is powered. Doesn’t really matter if you’re the only one using the machine and trust yourself to always remember to check if it’s pluged in.

I think this is rather unlikely to happen, but I should mention it:

There’s also some potential to create objectionable current, since neutral is already bonded to earth. And if the PE is pluged into a into a different outlet (or somehow else has a diffrent path to earth), you create parallel paths. There would be small diffreneces between those paths in resistance (and voltage). That means a tiny current can circulate between them, instead of going through the intended ground path.

Those currents should be small, simillar to what you already measured, but they create unpredictability (edit: worded this wrong, they don’t create unpredictability but rather are a sign of it, the unpredictability is caused by the closed loop to ground). If a real fault happens it could make the fault current split changing how a breaker responds. Also, if you have audio equipment, and the objectionable current path goes through it’s ground path you could get some noise/humming