A guess: if you need a constant modulation source and do not use the sequencer for other things a single step sequence can be used as a constant valued modulation source.
How is a one-step sequence different from just setting the pan value? I'm fully prepared to believe that it is -- I'm just trying to learn how it works.
To understand this, you have to know, that it's not a Pan setting.... it's the dreaded "Pan Spread" setting... when you use the Pan Spread, the voices jump from left to right, and it's this "hardwired" setting that you just cannot break... so no matter if you use single or layered sounds, if you set some Pan Spread, then the voice will bounce from side to side.
That means, that if you set up a stacked layer, and you set Pan Spread to say; +32 on both layers, then both Layers will bounce in tandem because you cannot set the Pan Spread parameter in negative values... If the Pan Spread setting had the possibility to be set in negative values, you could set one layer to have positive Pan Spread, and the other to have Negative Pan Spread... that would insure that one layer will allways sound at the left, while the other Layer will allways sound at the right... thus, if both layers contain almost identical sounds, you get a HUGE stereo perspective.
The only way to apply negative Pan Spread, is to do it via the Mod Matrix... one layer with possitive amount, and the other Layer with negative amount.
The problem with doing this with the sequencers is that the sequencer's step values cannot be bipolar.
But one thing to note is, that even though Layer A and B is sounding in oposite sides using the Mod. Matrix, the voices STILL BOUNCE! ... Layer A will still bounce from left to right, and so will Layer B... the only thing the Mod-Matrix trick does is to make sure that Layer A and B is bouncing opposite of each other... and not at the same side simultaneously... thus, if the Layer A and B sound is too different, you'll hear the bouncing.