It states that two boons *BB* or two banes {BB} may be used to recover or cause fatigue. It also states that boons and banes are 'fuel' and must be spent (unlike successes).
My question is, do you need to be successful in your hit attempt to use them as such? My second question would be, if there are boon/bane effects listed on the card, can you still opt to affect fatigue instead?
I would say, yes, you need to be successful, but that seems a little counter productive when considering banes.
I would also say that you may choose how you want to spend them, but I seem to remember reading something to the contrary (I just can't seem to find it at the moment).