Probably to exploit the so-called carbocatalysis originated by the coexistence of both holes and sp2 carbons... but I am not sure.

The electronic conductivity of the reduced graphene oxide is more than graphene oxide. But recent studies shows that graphene oxide based composite could be used as photocatalyst. 

You can check this paper

Roles of graphene oxide in photocatalytic water splitting

MaterialsToday,Volume 16, Issue 3, March 2013, Pages 78–84

Reduced graphene oxide has higher rate of electron mobility which  is the major factor in photo catalytic activity of reduced graphene oxide.

thanks to all for nice response on my query