I completely agree with TeraTask about efficiency. I'm learning Discrete Math right now, and I realized how can math is very useful to create an efficiency in our codes and algorithm! *Learned some Matrix*
I personally haven't used math application on my program, but I can see that the application of Discrete Math is just amazing!!! *Still full of mysteries for me though...

* but I can see that is is being used in many applications such as: figuring out different path in the network and which part is the most efficient by algorithm of numbers