there is a recommendation to use only flight detent position for the speedbrakes.
The reason,as i've heard, is this: the spoiler mixer is calibrated for two speedbrakes positions -retracted and flight detent. If you use them at a different position while in straight flight no problem will arise.However,if you do this in a turn,there is a chance for a wrong deployment of the spoilers during turn (to assist the ailerons) ,calculated by the spoiler mixer with an uncalibrated speedbrakes position. This can result in an sudden ,higher than normal,roll.
It happened to me once,not so funny,and since then, I use only flight detent position,and I try to extend and retract the speedbrakes only during straight flight
