I don't see how it can hurt. Not enough people have been churning business cards for us to know for sure, but by the time we know for sure it may be too late (since at least for personal cards, at BofA credit limit that's reduced before you cancel is available to subsequent cards within months, but credit limit that is on your card when it's cancelled doesn't because available to subsequent cards for over a year .

So, without knowing whether it works the same way for BofA business cards or not, I'd err on the side of caution and reduce credit before cancelling. What can it hurt, other than a few minutes of your time?