On the 737NG just because you command the engines to do something, does not mean they will respond instantly. You will see the "command sector" on the DU to reflect your input and the EEC's will then control the thrust retardation to avoid shock cooling or other unwanted consequences.
As the other posters allude, it is not a good habit to get into. I can't think of ANY situation where you would need to slam home the throttle levers, rather than slowly bringing them back. One day you will fly a type which may not have such good protection and it's good to learn sound operating practice now rather than later!
P.S. Apologies for thread bump didn't realise this was two weeks old!
Last edited by MrHorgy; 27th Aug 2012 at 21:38.
Reason: apologies..