I use shoot through umbrellas frequently and have yet to find a reason to go the softbox route. I can see certain advantages to a softbox such as easier control of light and especially less problem with lens flare, but they are far less portable and much more expensive. Are there other positive qualities that I am missing?

I am an amatuer that already has more lighting equipment than can be justified, but softboxes are recommended so frequentlty compared to umbrellas that I can't help thinking I am missing something in the quality of the light. That is besides square catchlights and controll.