Processing Fee?

I am confused about the processing fee; is it charged to buyers per book? Is it per check sent to the author? Is it per book order?

I couldn’t seem to find anything that really explained it.

Thanks so much =]

it’s too much bookkeeping to deal with small sums. Is it possible for Blurb to NOT cut the check until requested?

Doing this would cut into Blurb’s considerable margins. I’m certain they’d be hard-pressed to slant this toward the author’s advantage.