Rozkaz is much more powerful than Sz. Of course you can also use Rozkaz when there is no possibility to display the signal, but the Sz is the much more common way to do it. Rozkaz can be used for a much wider range of irregular activities, among them:
-allowing to pass the STOP signal (use it when Sz cannot be used);
-allowing for departure from the track without any semaphore;
-allowing for departure on the left track with non-suited line block system (use it when there is no W24 sign on the semaphore, or if there is but the Sz with W24 cannot be used);
-releasing the train from obeying automatic block signals indications (use it on Parzęczewo if there are multiple automatic block signal failures on the line, but make sure that the whole line is CLEAR. Driver is released from obeying the signals and any train standing on the line won't be protected);
-allowing to push the consist from active line (use it if you by any mistake depart the incorrect train and need it to push back to the station, so it enter tail first loco last);
-allowing to enter the closed portion of the track (if for any reason you need the train to enter the track closed by the D1 sign);
-allowing to pass the W5 sign by the shunter, and thus enter the mainline (use when the shunting consist is too long to clear the switches, but make sure that the line is CLEAR and there are no trains incoming, so you don't send the shunter for a head-on meeting with any other incoming train);
-and any other irregularities, which can be manually written into the fourth "INNE" (other) category. You can write there anything just to make drivers life harder for example: to order the driver to stop the train on the line at kilometer 12.345 and pickup some pizza and some crates of ZEW10, to be delivered to your signal box.
And also be extremely cautious when using Rozkaz. Improper use of these may result in you becoming a new meme on forum, or even receiving some Skarga in the system. It's best to practise them with more experienced dispatchers before you start using them, and then look how they write Rozkaz and copy cat