If I have a 17mm. Fillet weld on P1 and P1 which have root pass and 2 cover passes. Are there any disadvantages if I preheat and weld the root pass then let it cool down in ambient air and I preheat it again then weld 1st cover pass and do the same on 2nd cover pass compare with single preheat then root-1st cover- 2nd cover ?

Thanks