This is just a suggestion. The change would allow building and installing krusader with standard dev KDE building tool ./kdesrc_build without root privileges.
Without this patch 'make install' is always installing qt plugins into protected /usr/lib/qt/plugins directory regardless of set CMAKE_INSTALL_PREFIX. That means installing fails. With this patch, plugin directory is set e.g. to ${CMAKE_INSTALL_PREFIX}/lib/qt/plugins.
I realize that the removed setting is there for a reason but I cannot reproduce any problems. Also none of KF5 packages (including KIO with a lot of Qt plugins) have this setting enabled. Any info regarding this proposed setting removal is appreciated :-).