Whenever a car is designed, engineers have to consider a lot of factors. Depending on the targeted market and the kind of vehicle they want, they must consider performance, luxury, price accessibility, aesthetics or any combination of these factors.
In recent years, more fuel efficient vehicles have also seen a rise in demand. And technological advances can only do so much, so car makers try to keep things as light as possible.
The weight is important not only for fuel efficiency, but if you distribute it wisely, the performance of a vehicle can also improve. The best way to do this for a while has been shifting the engine placement. First from front to the back, and then to the middle.
BMW knows the importance of weight distribution too well. Its racing pedigree and overall performance of its vehicles can attest to this. BMW Canada even launched a video on youtube displaying the perfect 50:50 weight balance they struck in the BMW 1M coupe.