My Yamaha keyboard has what they call Performance Assistance Technology which up until recently I rarely used. The manual says it works with Songs/Midi files and specifically midi files with imbedded chords and melody like the included songs and other midi files like XF files. You can take a regular midi file and with PRSutility compute chords and it will work also.
I rarely play with midi files and almost all of my playing is with auto-accompaniment with styles making PAT next to useless for me. I play a few midis that don't seem to work well with auto-accompaniment because they have rhythm changes during the song or whatever and then I might use PAT.
However, the other day I "discovered" that PAT works with auto-accompaniment as well, although it doesn't seem to be documented anywhere. As long as you are in the Chord Mode of PAT and play chords with your left hand with a Style you can improvise(cheat?) to your heart's delight with your right hand. This makes it handy for an amateur like me to add an interlude, scale, instrumental, etc. to a song where I couldn't before. I know you pro's are really groaning at this but maybe someone else can find this useful like I do.

Which model do you have? I have mixed feelings about the Performance Assistant on the Yamahas. If my memory serves me correctly here I think they even added that feature to the PSR-3000. A feature like this I don't mind as much seeing on lower model boards for beginners getting the hang of playing the keys (although this features teaches a person nothing, and is just for instant gratification and the long term effect on the player is useless in my opinion), but for them to include this feature on their big dog PSR-3000 is just shooting themselves in the foot.

Arrangers already have a negative stereotype in the keyboard world, even though we all know some arrangers out there can hang with synths and in several cases put them to shame. Yamaha put the PSR-3000 back in the TOY department in my opinion by adding the Performance Assistant Feature.

You don't buy a $1,500 keyboard just to press one button and have the board do all the work. You spend maybe $200-$300 for something like this. The PSR-3000 costs more than the original Yamaha Motif now. You can get an original Motif for $1,200. The only thing I can come up with is maybe Yamaha added this feature to the 3000 just to maybe get those suckers who'd pay the price to have a PSR-3000 as their first keyboard. I do know of one person who told me he went to demo the PSR-3000 and the sales rep focused on the 3000's ability to do all the work for you. He even said the 3000 make the most novice player sound like a Pro. Hell the PSR-3000 sells in the Pro Keyboard Price Range. It's not a toy and should be marketed differently. Sorry to rant there. I guess I'm really not that big of a support of this feature.

Squeak

Squeak,
I have a Yamaha DGX-305. I can't say that I disagree with you about this feature but it is kind of fun to throw in riffs with it once in a while. I don't know why the PSR-3000 has it but it's probably as you said. It would seem to be useless to a pro player I agree.
Chuck