What goes on (that you are allow to share) in those places that requires so much time and energy? I can see building things taking a lot of effort, but is it just for theater that people put in so many hours in those places?
In investment banking, you usually work on a small team of 3-6 people. The work day is very different depending on whether your team is currently working on a deal or is between deals and pitching clients.
If your team is on a deal, then there could be honest-to-goodness work keeping your team busy for 100 hours a week. Tasks include preparing the materials used to market your client to potential investors (including financial models, presentations, and dense official offering documents), managing and attending meetings with investors or the Board, running down data requests, and diverse other things.
Most of the bullshit work comes in when a team is between deals. During this period, the senior members spend a lot of time working their connections at potential clients while the junior members prepare "pitches" - presentations designed to convince a company to do a deal. Junior employees are expected to be at the office when their superiors arrive and stay at the office when their superiors leave. When I was working, I might start a typical day by finishing up a request from the day before, then have absolutely nothing to do for 4 or 5 hours, and then receive and turn around assignments from sometime in the afternoon until the evening. The boss would make his last calls around 7PM, which is when I would get my last batch of work for the day. I would work on that for anywhere between one to thirteen hours and then head home (or not, if it was 13 hours).
The culture at an investment bank is very unforgiving. An employee must be a competent worker to survive, but he must also be sure to keep up appearances. Half of an employee's pay is paid in an annual bonus, which is determined by a mixture of objective and subjective factors. It is not enough to be a good worker, an employee must also make sure he looks like a good worker - which entails being seen in the office a lot. The time of a junior employee is not considered valuable, since they are well overpaid compared to their peers their bosses feel like they should be willing to take unlimited shit without bitching. Managing Directors think nothing of asking an Analyst to do something on Sunday when it pops into their minds, even if the work could easily wait until Monday morning. An MD will also have no qualms about asking an Analyst to start on something at 7PM when he could have told him about it hours earlier. You have never seen so many bitter 23 year-olds as you can find at an I-Banking office.
In exchange for most of your life, an entry-level employee is usually compensated well for someone just out of college. I'd estimate the mean analyst on the street earns $120K in an average year. I wasn't on the street, but I'm not working right now thanks to my savings from my days as an I-Banker. If I could do it again, I probably wouldn't. I like where I am but those were a bleak, desolate 2 years and the angina hasn't completely faded away yet.
It is what it is. It is cool to work with hard-nosed, business-minded, sharp people. I enjoyed sitting in on meetings between Private Equity funds and the executives of the companies we were trying to raise money for. I learned the function of all the players in the financial market and I got to stay in nice New York hotels on someone else's dime. I made good money. But it wasn't for me, so it was slowly wearing away my health and sanity.