As said previously, a lightened flywheel will spin up quicker, particularly noticable when revving and stationary. This then feeds its benefits into when you accelerate as the engine has less rotating mass to shift in order to gain revs which in turn gives you speed. The downside is if you lighten too much then you get reduced momentum so you will tend to lose more revs when changing gear. As with most mods they usually need coupling with other mods to make them effective - so if you fit a quickshift kit then you may gain back what your losing when changing gear but you'll be back where you started before lighteneing.
I have never run a lightened flywheel on my golf but my old mini had one in and these were my observations, of course it will be more noticable and obvious what effect things are having in a car such as a mini (older, simpler, lighter etc) but just thought it was worthwhile mentioning it. TBH i don't think its worth it for the golf - changing form a DM setup to the G60 is good enough IMO
