Does using a sponge in a brioche make a difference?
In general, preferments of any kind are used for several reasons:  


They activate questionable yeast to make later rises more effective
This is less of a concern these days with freeze-dried yeast and freezers that keep them viable forever.
They promote a more open texture
With the extra time to rise and distribute themselves, the yeast blow the dough up into large pockets instead of a bunch of small pockets. This will happen less with a very wet preferment like a sponge but it will still make a noticeable difference in the texture.
They enhance the flavor
The longer the yeast are able to work the better the bread will taste. If you put your sponge in the fridge overnight the yeast will slow down but keep working and in the morning you will have maximized your flavor.


With all of these reasons the choice is totally yours. You will see a definite improvement using a preferment, especially with something like brioche that should be rich and flavorful. If you are in a hurry though- a fast brioche would be better than none at all.