People. The nature of the business of consulting means that all your coworkers, especially in your practice (department), are also your biggest competitors. You can't really trust the people you work with or those managing you since everyone is trying to maximize their own personal profit. Think of it as a zero sum game, someone else's success takes away from yours - or so the thinking goes. If you know that's what you're getting into and believe that's a situation you'll thrive in, power to you. I personally did not enjoy this environment of never really having coworkers that I could trust.
As other reviewers have mentioned, your holidays, vacations, and sick leave all count against you when metrics are generated to compare you against your peers. Even using working hours, to do company required trainings, counts against your profitability metrics. The firm only wants you to do billable work during company time and everything else, on your own time if possible.