Well, it would seem that a filter on the back of a tank would only mix up the water at the back.
I'm getting (or trying to get) a small herd of albino Khuli loaches, and I figure that if I got some type of a setup where there would be a current along the bottom of the aquarium, more oxygen would get into the hiding spaces that I'm constructing in the rocks. And overall, who wouldn't like to surf along a current once in awhile?