use of Insulating Washers

[Salmon Trout]

there seems to be no need to "ground" the board to the case.

It would probably help to keep with RFI emissions down. It may be an FCC (or local equivalent) requirement.

[Lisa_maree]

Hi Guys,

Thank you for giving so much thought and input into my question. It all makes great reading. Thank you again

[lectrocrew]

Well, I don't know if I'd call it great reading but I,ve learned a few things. It's a shame we haven't really answered  your original question:

Is there a good reason for doing this ? And if it is necessary why don't the manufactures use bushes in the holes.

[Geek-9pm]

Best answer was by Patio and is a Classic answer.
"It makes it easier to take the board out."

That answer is piratical, accurate verifiable.