However, turning off Focus tracking with lock-on will cause anything getting briefly between your camera and the subject to draw the attention (focus) of the camera. Only turn lock-on off if your subject will not go behind some other object while tracking, or a brighter, closer object won't enter the frame with your subject, or you could lose focus on the subject. The camera waits to refocus for a time you determine in settings if it loses the subject briefly.
It only speeds the camera up to not use lock-on because the camera no longer worries about staying with your subject when something gets in the way. It does not have to use extra processing power to stay with your subject even if it is briefly blocked from view.
============================================== Darrell Young (DigitalDarrell) www.pictureandpen.com "Better too many words than not enough understanding." ==============================================