Of course you'll need all 4, because you'll want to put something under the coffee cups when you have guests :-) MOST users will never need much or any of the source code, unless there are re-compiling the binutils pkg, for instance, with their own personal patch. MANX users will compile their own software, but I dare say it's usually something extra, that's not offered in Slackware at all.
If you REALLY care about what you REALLY need, with just 22MB- less than 10 pkgs, you can install a system that meets the definition of Slackware. With a 42MB system(that's with kernel modules and pkgtools,etc.), you can create a fully extendible Slackware. Below 20MB you can create a Slack that runs, but doesn't even have elvis. nice secure distro that can only be altered by someone who knows how to create config files with 'cat'!
You can read about the Crazy 3-Legged 20MB Slackware HOWTO and other more reasonable Minimal install strategies by following the link to Minimal Install Index on
www.amigolinux.org
The other day I had an idea for a complete linux system under 300k. 4 distros on one floppy anyone? HeHe
If you are no programmer and don't plan on becoming one, you can easily leave out ALL of these Slack Directories: /e (emacs), /d (compilers and stuff), /f (the linux DOCS, if you choose), /k (the kernel source), /t (tcl/tk stuff). And of course, making a hard choice between gnome and KDE will cut out +-200MB.
I never install from ISO's, instead I start with an install of ZipSlack and add in what I need to get to a nice 200-300MB install, for comfortable browsing, e-mail and text editing/light graphics work. Since I DO compile a lot of both C and C++, my 'full' installs, including the 150MB or so of kernel code, reach the 500-700MB range- tops.
My hat is off to anyone who can come close to learning to use and having a chance to make use of 1.8GB of software... before the next update comes out!