google analytics – Exceptions of different scope combinations in GA

I am studying about the scope in Google Analytics and, obviously, I have read that we shouldn’t combine different scope metrics and dimensions. However, I have some questions regarding the exceptions allowed.

For example, we have the following combination:

Bounce Rate by Page (session-level metric by hit-level dimension)

I have also read that we should never combine session-level metrics and hit-level dimensions, because when combining any session-level metric with a hit-level dimension, the metric will only contain data from the first hit of the session. So, even though there are some exceptions, this shouldn’t be one. However, in this case we do have such a combination. Why?