To be honest, I wasn't aware of the "Local Ratsnest" option until I saw this thread. Or maybe I had used it without realizing it was enabled.
However, I have DEFINITELY exploited the underlying concept, often invoking the "Highlight Net" feature at least once while placing a part, or laying down traces after placement. Sometimes I click on two or more nets in rapid succession, trying to visualize the entire connection constellation for a given component. Sometimes I click on the pads or traces in the vicinity of where I am trying to route a trace, to better understand the interactions among nets running through the local area where I am working.
So yes, I am in favor of being able to highlight or emphasize portions of the overall ratsnest. As shown in my examples above, there are justifications for doing so on a per-footprint basis, or a per-region basis, as well as the traditional per-net basis.
On a related topic, it could be helpful if the "Highlight Net" feature selected a net by clicking on a line in the ratsnest. Sometimes I want to know, "What net is associated with this particular unrouted connection, and which components does it connect to?"