Although I prefer the flexibility of styles every once in awhile I'll come across a tune that's hard to re create using auto accompaniment.

Sometimes you need song specif bass lines, drum parts, or stops and starts that are hard to do with styles. You'd may be surprised how many songs that sound like simple 4/4 will throw in a measure of 2/4 (the quirky 2 count) Songs like "Purple Rain" and "Pretty Women" come to mind. Many Korgs and Ketron keyboards have a reset botton for instances like that so the beat doesn't get turned around.

Another thought: Although you may have more control with styles, it can actually look visually fake form an audiences perceptive. When playing with styles your left hardly has to move at all to generate full sounding accompaniment. When playing over backing tracks you are able to play full two handed piano style accompaniment that maybe be too complex for the auto-accompaniment on an arranger keyboard to recognize.

There's pro and cons to both auto-accompaniment and backing tracks. No need to limit yourself to one or the other.