In another topic my good friend Scott Yee wrote that he likes the Yamaha PSR 2000 even if its styles are short (usually 2 bars), because that's the way a real drummer plays; he added that you can make a style come to life by triggering fills (with a pedal) or playing manually drums (via dedicated pads).
I, on the other hand, am accustomed to Roland styles, which have longer loops (at least 4 bars, but often more, especially in intros and endings) and, analyzing the difference between Roland styles and imported Yamaha styles (even those from PSR 2000 and CVP 209) have come to some conclusions: the most obvious is that, if a style is recorded live (and not step by step), longer loops allow for a greater degree of variation. This is of course more evident for melodic instruments like a piano or a guitar (where you can play a slightly different riff for each bar), but even a bass player or a drummer can introduce a greater variation in the performance in a longer loop. Just think of the intensity of the single percussive hits or the distance between single hits; these are not always the same: it's just like a drummer or a percussionist is musically "breathing" while he plays or there is a "wave" going up and down in the performance. It is often said that some drummers or percussionists play ahead the beat and some behind it and this becomes evident with time, i.e. the length of a loop; I think that all these variations are more difficult to reproduce in a simple 2 bar loop.
To summarize, I think that short, 2 bar loops are more prone to sound lifeless or even sterile (the famous "canned" sound) and I would go even further to add that, with a series of long loops (recorded live by ALL the musicians) it would be possibile to capture the realism of a live performance even for jazz styles and make a style really "breathe"; of course you could always add your fills and throw your odd percussion in (via dedicated pads), but this would be like a cherry on an already tasty cake.
Obviously nothing can substitute the realism of a live performance, but, since we are talking of arranger keyboards I wish that one of the great improvements of the next generation of arrangers could be to have more internal memory to allow realistic styles with long loops, maybe combined with sampled patterns, the way Ketron (and GEM too, if I am not mistaken) are already doing.
Regards,
Andrea