The KDE community maintains a lot of cool (and sometimes cross-platform) applications for the GNU/Linux desktop. Most end users, however, only know and run whatever default subset and configuration of those applications was packaged as "KDE" by their distribution.
Of course, there's nothing wrong with this. The more people manage to use free software only because of that work of pre-selection and integration, the better! Still, it pays to know and try less-known KDE programs that might be much better for you than their default counterparts. One of these is Krusader -- a twin-pane file manager that could be faster than Dolphin on older computers or just a better match for your computing habits.