shower supply question

just wondering on my shower supply line there is a 1/4 flexable copper tube tee'd into the supply line a few feet before the shower head. just wondering what this is and where it goes too?

 

i followed this tube and it is delivering water whenever the shower is on to a drain in the basement, this appears to be just a waste of water (esecially hot water) has anyone heard of this before and is it nesesarry?

 

It sounds like some DIYers idea of keeping the trap from drying out and causing sewer gas to finds its way into the house.
I would eliminate it and use RV antifreeze in the trap to prevent it from drying out.