Torx provide a larger clamp bolting surface area relative to the amount of torque one can apply to the fastener. They also take a small tool so there is greater clearance - this is important as modern car designs work to make more compact areas. As an example I remember the 80's Fox Mustang 5.0 exhaust manifolds had huge crimps in the runners because of the need to get the tools in place to tighten the exhaust stud bolts. It's why we see Fel-pro, for example, having torx head bolts versus the shitty hex bolts I just pulled off the QR25DE Nissan the other day in my garage.
Torx are great, and if you are working on BMWs, I highly suggest full and complete sets of male and female torx sockets (shallow and deep) along with torx box end wrenches.
Filippo