No, partly because fireflies take a certain amount of time to "charge" so jumping mid cycle might not be plausible physically.

So what this line does (which is in the section of code where a flash alters the fireflies around it) is that after advancing the other fireflies clocks, if any are over 1 then it puts them in the right state to flash on the next time they're evaluated. If you mod it, then you would have the logic:

"if I'm a firefly and see my neighbour flash while just about to flashing myself, don't flash but reset my clock to part way through the cycle"

rather than

"if I'm a firefly and see my neighbour flash while just about to flashing myself, flash as well"

Edit - setting it to one ensures that each neighbour can't keep adding to the clock, advancing it to a random point in the cycle.