cardio before or after weight/strength?

or does it not matter?

and if it does, why?

Like everything, you will probably get both sides...here is my uneducated opinion...I used to do cardio first and someone at the gym told me to do strength first because I wanted to build muscle.  His reasoning (which "seems" to make sense to me) is that you want to use your energy stores to ensure you can lift as much weight as you can to build muscle.  Assume you deplete or lower your energy reserves while doing this, then your cardio workout would tend to draw more on fat reserves, which is what you are trying to achieve.  Reverse that and you are doing cardio with your initial energy stores and not fat reserves, AND you probably cannot lift as much because you are more tired after doing the cardio.  No a doctor, but it sounds reasonable to me...on the other hand, I see some pretty buff muscle heads doing cardio first, then lift, so go figure.

lift first, then that will make your cardio even harder. Which will mean your body has to work harder and burn more calories. Where as lifting burns less calories, so you want to be at full strength to lift all you can.

weights first. Can't remember why but that's what my rowing coach reckons, and he was an olympian