Good for turbine helos - keps them clean by removing the environmental erosion deposits. Other things to consider though:
Flying for too long in heavy rain can cause blade erosion hence cost for replacing the erosion strips. Sometimes these strips break down unevenly causing the rotor to become unbalanced, then you'll need a track and balance kit on the blades agaian cost.
Wipers are useless above say 60kts - waste of time fitting them!
Heavy rain gets into places you never knew existed giving rise to spurious captions etc.
Dont fly for prolonged periods in rain in small helos, and reduce speed to about 2/3rds Vno.