I'm also at a Big 4 firm and although we have a policy that allows for the flying home or bringing someone else out if you choose not to go home, its really all project-dependent.
For example, I've had projects where I've flown NYC-Seattle on Sunday night and returned Friday morning, which meant all day Friday was spent traveling. Had I wanted to bring someone out to me, I would have been able to do so no problem, as the refundable ticket (then) was about $1200, more than enough to cover a couple nights and some non-refundable travel for my guest.
Once the project is international, things get a bit more murky. There's no way you're going to be able to come home from Asia every week, even if the company was willing to pay. In cases like that, regional travel and other things are allowed.