A lot of combat athletes still use road work and other long slow distance (LSD) methods to condition themselves for upcoming fights. If you look at this logically what energy systems predominate these events?
MMA fights are 3, 5 minute rounds or 15 minutes of work, clearly the aerobic system is dominant therefore you can argue for the inclusion of this type of conditioning work. However if you look at the training of these athletes they usually have well developed aerobic systems in place due to the sport specific technical training that they go through.
You can split combat sports training into the following blocks, forgetting the strength and conditioning elements temporarily:
Technical Work- Informative elements such as learning and developing techniques
Isolated sparring- not full intensity
Light Open Sparring- again not full intensity
Heavy Open Sparring- Full intensity
Of the above elements when you put a heart rate monitor on people in these sessions all of them except short and heavy sparring are fuelled in high proportions by the aerobic system. Therefore my feeling is that this is more than covered in the everyday training routines of these fighters. It is the anaerobic systems that need the most development and you tend to see the most improvement in a pre fight cycle.
The anaerobic systems are best developed through strength and power training, power endurance circuits as well as more extended circuits when the time is right. The main argument for roadwork and LSD is for weight loss when high intensity sessions are an overtraining risk. Even then I can think of better ways to lose weight than LSD training. If you are an MMA or combat athlete make sure your training is not based around steady state aerobic work as this will not have as big an impact on your performance as working at higher intensities for shorter amounts of time and manipulating recovery times to provide you with the adaptations your looking for. Plus its so much less boring as well which is a big deal if you have an attention span like mine!!