walk- in or jog -in starts


For years I have seen many coaches in many programs use a flying start for all of their sprint/speed seesions. I have also heard some advocate a run-up or short walk in for evry sprint. When doing 20s, 30s or even 150s for that matter , if Iam not specifically doing fly work, I go from a standing or 3pt. start. What are the specific benefits (if any) from have a run-in or walk in to all sprint intervals? for instance a slight 15 meter jog in for a full 150 or a slight run-in for 100m. Keep in mind, I am not refering to fly work specifically. I get the point of that. I just walk-ins, jog-ins and the like. Can you explain? Thanks.