The biggest benefit of Slackware is that you can upgrade things at will. There are no surprises if you have to go upstream and do the "download/configure/make" dance.
In Ubuntu/RedHat, everything works if you stick to the package system. But if they are too slow (or you need different compile-time options) it's not always easy to "do it yourself". Grabbing a fresh copy from upstream will often break in subtle ways because of changes made by the distributor. (In fact, that's what makes moving between these distros a pain.) They do everything from moving around config files to adding custom patches to changing the name of services! (ssh vs sshd, apache vs httpd).