Using the magenta circles

A friend recently asked me to explain the magenta circles seen around
numerous airports on sectionals. It got me to thinking about how
useful they are. Personally, if the weather isn't good enough to fly
VFR in Class E airspace, I'm not going to fly VFR, even if it is legal
in Class G airspace. So, for me, it is pointless knowing where the
boundary is between Class E and Class G airspace.

But I was curious to know if there are pilots that take full advantage
of this distinction. Does anyone actually make use of the Class E/G
boundaries depicted on sectionals? If so, how? I suspect the most
common use is doing T&Gs in the pattern below 700 feet AGL when the
weather is marginal. Other uses?