For the past 20 years, I've been using PTR records as the basis for
patterns that are then classified according to various criteria:
assigment type (static/dynamic/mixed) and various other things like
NATs, infra, resnets, shared and dedicated webhosts, and so forth.
Turns out it's a pretty useful way to decide whether to accept mail
from an end user node or reject an ad click from a datacenter, among
myriad other uses.
Part of the process involves trying to determine whether generic names
that don't indicate assignment type are static or dynamically
assigned, and one helpful clue is rwhois that accurately reflects the
size and hopefully registrant of the block with that naming.
Of course, with WHOIS gutted, and rwhois servers that don't work or are
nonexistent, my job here is complicated enough. It really helps to be
able to know what I'm looking at. So YMMV but I find accurate, detailed
rwhois AND PTR records extremely useful, as do the folks who license our
dataset, which at last look covers around 97.4% of IPv4 PTRs (for fun,
take a look at a Hilbert map I did of our coverage, and the following
example PNGs showing our overall coverage per /8 and the breakdown of
which IPs in which /8 have PTRs and how they are classified).
enemieslist: coverage map
Coverage by /8:
Classification breakdown by /8:
Basically, you may not care but there are a lot of companies and
researchers who very much do.
For another example of why this matters, we were customers of a large
business class cable company from mid-2007 through early 2013, and as
we were doing some small-scale hosting, we asked for and got a /27
with custom PTRs assigned. They're still there. Oddly enough, I asked
hostmaster@$BIGCABLECO today to remove them again (I do it every few
years out of a triumph of hope over experience that is never requited).
Maybe it will today, I don't know. But if you ever see abusive traffic
from a block that has been assigned to a NC community college whose
IPs have PTRs in either of the following domains, it wasn't us.