There is no need to do so, but as I’ve said above, different applications may handle interrupts differently. Some will save their state to the drive and gracefully exit when they receive the terminate signal (SIGTERM), some won’t. And some will outright disobey the terminate signal and will have to be killed (with SIGKILL, which does not give them any chance to save their state).
So, it depends on what your desired outcome is.
On KDE Plasma, there is a also “save session” option that makes the window manager remember all running applications before terminating them so that they can be launched on the next startup (trying to restore their state, if possible). It will also run any scripts you may have in ~/.config/plasma-workspace/shutdown/. This won’t happen if you shut down with the shutdown or poweroff commands.
If you’re interested in knowing how to shut down your computer from the terminal emulator on KDE Plasma in a way that is equivalent to using the GUI, read this post: