Lighter flywheel will allow the engine to rev up faster and rev down faster as well, both engaged and disengaged in gear.
while it won't give you any horsepower, it won't eat as much to turn the roatating mass to get momentum.
On down shifts, using the engine braking, it will wind down fast as well.
it can make driving 'jumpy' as clutch-in's cause the revs to fall much quicker than you will be used to.
If you're planning to build over time, i say go for it.
If you're going to stay mostly stock, i/h/e, it's not a great streatable set up and could get annoying in time.