Its learning potential is very large.
As someone once wrote:
Study RedHat, you will have learned RedHat
Study SuSE, you will have learned SuSE
Study Slackware, you will have learned Unix.
One thing that it has over probably all other distributions is its stability in terms of software selection. It still defaults to Lilo over Grub, it didn't switch to systemd, and installing Slackware 15 or 14.2 when it comes out will be exactly the same experience as installing slackware 14.1, or just about any version preceding it, I'm sure of it. :)
It has one thing to make it genuinely notable: it's the oldest surviving Linux distribution out there.
Practically, it's barebones and basic yet functional enough to do whatever is needed. It's extremely easy to make Slackware into whatever kind of system you're looking for from desktop to server.
As for other uses... using it to reply to this comment right now.
There is no lack of package management. There is a lack of automatic dependency resolution without third-party additions. This is nowhere near as debilitating as often presented by outside observers who have never tried the distribution.
YMMV, but I've ran into circular dependencies and conflicts in addition to configuration updates rendering systems unbootable multiple times on distros like Debian with their non-transactional resolution heuristics that make your life easier, until they don't. Slackware's spartan package management has not failed me once, it's rock solid no matter how much you thrash your file system hierarchy. In addition, when I want to install SlackBuilds, I have never used a more convenient package manager than sbopkg before. Dependencies can be cleanly recorded and built with queuefiles.
Slackbuilds.org will tell you if one of the packages there has dependencies that aren't in Slackware. Typically installing them is not onerous.
In that sense it is practical, not sure if "notable" as there are many other more popular distributions these days.
I hate Ubuntu, RedHat, etc... Everytime I use them, I feel like I'm fighting the GUI. Ubuntu, for example, I could never figure out how to change the IP address without using the KDE GUI. On Slackware it's as easy as editing /etc/rc.d/rc.inet1.conf
I resist Ubuntu, RedHat, etc... because it forces you to become familiar with that distro's way of doing things. And there in lies the rub. As more and more distributions of Linux come about, I see a fragmented Linux world.
So, in short, I guess you could say I stuck with what I learned and know from years back. I know that at start up, the stuff inside /etc/rc.d/inet1.conf are parsed and fed to ifconfig for static IPs.
my 2 cents...