Thanks a lot, but I should post my macro for clarification. I made the following Fire macro. I'm not sure how much DPS loss it is but I don't think it is huge.
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/ac "Fire"
/micon "Fire"
I don't intend to cast Fire continuously. I make it executable before GCD is done. I use it just like ordinary actions.
I tested it as THM at the Hall of the Novice DPS Training Exercise 4: Avoid Engaged Targets. There were not much difference in clear times. I find it more reliable than the ordinary action when I cast Fire after I move. If I cast Fire before I stop, unmacroed one is interrupted and macroed one is recasted immediately after I stop.