It's called Complex Training (both at the same time) but is very taxing on the CNS and can only be implemented so often and needs to be done so properly (to allow for recovery and quality in following workouts).
Complex training can be beneficial because combining the two forms of training can potentially result in better gains than when done separately. This is due to the increased motor recruitment seen in explosive exercises when they are preceded by heavily loaded exercises. This however is an advanced training method and should probably be used sparingly.
It would depend on the volumes used and the level of the athlete but 2 or 3 mesocycles a year; 1-2x per microcycle might be a good starting point. Having said that, I can't say I've ever really pushed the limits with this type of training. I just notice that when it's incorporated it can be very taxing.
We've used it similar to the parameters Mike outlined. Have had very nice success with our jumpers and sprinters when used as part of meso right before or cutting into meso before our champ meets.
It is very taxing and needs to be limited to one meso, overtraining can occur quickly if left in to long.
