For me, its a question of time. I can either do the work that has to be done by a certain deadline, and bill later, or bill with the work and do less work (or work more hours a day than I'm already putting in). For me, I think the answer lies in getting a billing system that can quickly and easily tally up the hours and costs so I can take an extra 5 minutes and bill. Then again, that precludes a long discussion with the client when delivering the return, or requires a follow up bill. I'm still looking for the answer. Let me know if you find it.