Makes fairly rational sense -- in addition to the hard deliverables provided by professional services firms (market studies, fairness opinions, consummated M&A

Makes fairly rational sense -- in addition to the hard deliverables provided by professional services firms (market studies, fairness opinions, consummated M&A transactions, etc), their "product" is to a great extent the warm-n-fuzzy feeling that clients get from the general perception that a bunch of intelligent, highly educated and broadly competent, insecure overachievers are burning the midnight oil to triple-check that everything is going to plan and there are no contingencies left unexamined. As such, on a meta level, the "product" in this regard is not some kind of impartial measurable standard of client-related vigilance, but rather, constant reinforcement of a perception in the client's mind. And so, it's totally rational that, for example, investment banking associates will always respond to a late-night email from the client's internal M&A guy or corporate development lady on the same night the incoming email was sent -- even if it's an email of the "hey no need to respond to this, just wanted to make sure I sent you the attachment" variety. Maintaining the perception that someone is always watching the store is paramount not only in maintaining client relationships, but also in justifying high fees.