The purpose of the bands for rows is different than it is for things like deadlifts, squats, and bench presses. For those exercises, bands mimic the strength curve, so they provide less tension at the bottom portion of the rep where you're weakest, and provide incrementally more tension throughout the rep as your gain a greater mechanical advantage.
For band-resisted rows, though, the tension is actually greatest where you're the weakest, at lockout. (Plan to use less weight than you would for a regular row.) This makes for one hell of a contraction and fries your upper back and lats.
To maximize the effect of the bands, hold each rep for a second at the top.