A good references for current's effects on attached algae on plants:
John A. Strand, Stefan E. B. Weisner, Wave exposure related growth of epiphyton: implications for the distribution of submerged macrophytes in eutrophic lakes, Hydrobiologia, Volume 325, Issue 2, Jun 1996, Pages 113 - 119
This study showed that intermediate wave action had a positive impact on plant growth, which a negative impact on periphyton(attached algae).
Low wave action had a positive impact on perinphyton but intermediate affect on plant growth(can you guess why? No/less CO2 with lower wave action). high wave action rips the plants up and they cannot grow there and no plants nor periphyton was found at these sites.
In general, the highest biodiversity is found where there is an intermediate disturbance level. This can be seen in the intertidal zone of marine systems and most anywhere in ecology. The intermediate disturbance hypothesis is the term used to describe this effect(Connell 1978). It is wide ranging and explains why some locations have high or low diversity of species.
This one is good as it shows that simply swirling a plant around it water for 90 seconds can remove 80-90% of the epiphytes growing on it.
So fluffing a tank up every few days can help.
Zimba, P.V., &Hopson, M.S. 1997. Quantification of epiphyte removal efficiency Zimba, P.V., &Hopson, M.S.  Quantification of epiphyte removal efficiency from five submersed plant species. Aquatic Botany 58:173-179.
Connell, J. H. 1978. Diversity in tropical rain forests and coral reefs. Science 199: 1302-1310.
So what might we conclude here?
Good current is helpful.
It physically removes algae and makes it hard for them to attach and colonize.
It also allows the CO2 mist to get blasted all over, it also reduces the boundary layer around leaves so the plant has more access to the nutrients in the water column.
Not too much though, but an intermediate amount.