I personally don't see the purpose in BDC reticle scopes. It's a good thought, but in practice it's imprecise and limiting.
A BDC is designed for a set load (specific bullet at a specified and contrived velocity). I can't imagine it's very often that a factory load shot through your specific rifle matches up perfectly with the BDC reticle. Changes in environmentals, such as density altitude, will change the ballistics of your load and then you are off from the BDC (if you were ever "on" to begin with). If you decide to change bullets, powders, different factory ammo, etc. who knows how well that will line up with your BDC reticle (even though it probably didn't line up correctly above anyways due to the above mentioned factors). Then you have to account for SFP if your scope is that - your magnification will completely change how the BDC reticle works. If it's in SFP, you have to shoot at one specific magnification or else it's pointless. That in itself is very limiting.
It's a fast but pretty imprecise system. If you are shooting big targets at short ranges (say ~400 yards and in), I'm sure you can get away with it, some people are perfectly happy with them. I myself much prefer a mil reticle of some sort (current ones are SKMR3, AMR and MSR reticles), with hard data/ballistics calculator. A BDC reticle has much more limitations then a mil reticle with good ballistics.