[morzh]

I always power my radios through an IT while it is in restoration mode.
While Steve is correct in describing the power transformer function, the isolation might fail without the transformer stopping to function as transformer if it has no short turns or opens. However small is the chance, it might happen and it does happen, and I saw it happen, so I use IT on all my radios while working on them, and then when they are in cabinets and on the shelves, they get powered directly from outlet.

I'd rather be safe than sorry.