It is good as a backup bow, rather than a primary weapon.
I don't quite understand that. Why use a bound weapon if you're carrying around a better physical version of it?
One of my favorite characters was a conjurer who carried no physical weapons at all. She used a bound bow and bound sword, and never had any good reason to carry the "real" versions of them. The bound bow delivers damage similar to an Elven or Glass bow, but is able to harm enemies which resist normal weapons. Its damage is not far below that of an Ebony bow. That makes it second only to a Daedric bow in terms of overall usefulness, but the Daedric bow weighs 22, while the Bound bow weighs 0. Plus it never needs repair.