Usually the ND filter is on the lens because you want to cut down on the amount of ambient and flash coming in. Ordinarily you wouldnt want ND filters on a strobe in the daytime as you want to be able to overpower the ambient with strobe power. You could use those to reduce the strobe power when you dont have to worry about the ambient, but if thats the case you can usually just power down and use a modifier.
Ty that makes a lot of sense (smacks head) 


















