Am I unusual in that I always net with my match bat? Given that I don't have multiple copies of the same Bat I always assumed it would be beneficial to use the same bat.
why use a net bat? I can think of several different reasons:
a) to pro-long the life of your match bat. If a top end bat has a lifespan of a thousand or so runs, why waste them on fake runs in the nets?
b) if you net on a different surface to the one you play matches on. For example, we play on grass tracks, but net on an artificial. As the net is bouncier and quicker than a 'real' track I tend to use a lighter bat.
c) to train your body - i.e. Glenn Mcgraph and (more credibly) Paul Collingwood have been known to use extra heavy bats in the nets on the theory that when they use a lighter match bat they will be able to generate greater hand speed.
There are probably a whole bunch of other reasons other people might be able to think of...