While true that PS1 is not command control, there is one benefit to using it with either a Z4000 or a DCS TIU/remote in conventional control mode on the variable channels.
This allows you to access the various combinations of throttle adjustments used to access PS1 features much more easily than manually by hand.
While a lot of those features are not something you might try to access every operating session, doing a manual "throttle high to low" cycle for 25 times by hand is tedious and ripe with opportunity to mess up and have to start over.
That's a random example, I have no idea if 25 is an actual valid command, but the number can unfortunately be that or something even higher - I recall 39 as being one of them, I think. ("darn, I waited too long when my wrist got tired on cycle 22 - lets start over...one, two....."). The Z4000 or TIU will raise and lower the voltage to the track automatically for such features when you program the buttons on the Z4000 or use the soft-keys on the DCS remote.
Also, there is a lot of transformer compatibility to consider. I'll let others go into more detail there, but as a single example, I recall it doesn't play well with an old TMCC CAB-1 and PowerMaster (original version form 1995 , at least). This is pure Conventional (with no command base added), but the PS1 engines won't like the "chopped" waveform type. The engine may move, but it will not likely react properly to special features like bell/horn button press combinations.