Newbie...Christmas Tree question.

[Makeall6]

I am new to the site and enjoying it. I have recently renewed my interest in the sport and I am trying to understand starting line procedures. I raced an L/S decades ago and it feels great to start enjoying this fantastic sport again. Here is my question. I was told how auto start works by a friend. Once three bulbs are lit, the other lane has 7 seconds to stage or he/she is timed out. And once all bulbs are lit, the tree will begins the countdown at varying times so drivers cannot "read" the tree. I get it...so far. But I wondered why the starter is holding a switch if the tree is automatic. So I asked the starter at our local strip (Norwalk). He was very friendly and said that he "arms" the tree when both pre-stage bulbs are lit. So far so good. But, I was watching ESPN coverage the other night and noticed that the starter Mark Lyle was actually launching the cars with that switch. You could see that once all cars where staged, he would hit the switch. I am confused and would really appreciate some feedback from you folks on the forum that really understand the sport.

Thanks so much.
Tom