This topic might sound silly to some of the participants here but in my experience there are a lot of questions about this concept. I queried a FOI about it, once, and he told me that it had raised more questions than it had answered. I queried him because a CFI at a country flying school had told me that it was illegal to fly through an adjacent R area, even though the R area was deactive.
I thanked him for his advice but thought bulls**t. Called the centre airborne, they said it was deactive so flew right through the guts of it. Gave me a boner to do that. Doesn't happen that often these days.