i always thought that HIIT provided more of an 'afterburn' effect just as weight training does. however long, slow sessions do also give this effect but no where near as much
iv found as long as you have a healthy lifestyle you will generally lose fat until a point, when you get there then you need to start killing the calories.
personally iv found this works:
10-15 mins of HIIT on the treadmill
30-45 mins of weight training, using compound movements to target as many muscles as possible
20 mins of a low intensitycardio exercise such as a cycle, slow jog/fast walk.
the ideas behind this is that the HIIT uses your stored glycogen, the weights build muscle and tone nd the slow cardio burns the fat. if you didnt do the HIIT your body would use gylcogen and not fat when doing the low intensity cardio.