If someone is using only strobes in a room with little or no ambient light what is the advantage of using slower shutter speeds for still life. I've read a leaf shutter adapts to most shutter speeds up to a certain point , but isnt a flash of light the same speed no matter what?

I've read of many people shooting largeformat and using strobes and stating that they rarely shoot above 1/60 of a second. Ifs there's no ambient or LED's being used in conjunction with the strobe then what's the point ?

If the modeling lamp doesn't dim after firing I can see the film soaking in a bit of the photons from that but in a completely dark environment wouldn't exposing the film to complete darkness simply increase contrast and grain?