'Rules dieters' find limitations oddly freeing, because the restrictions create a framework that's easy to follow. Essentially, rules dieters don't do well when they're let off plan, mainly because they are usually emotionally attached to food in some way.
Strictly speaking, intensity in the weight training context refers to the amount of work required to achieve the activity and is proportional to the mass of the weights being lifted - that is, how heavy the weight is relative to how strong you are.
Full-body workouts are great for someone who can only train a few times per week, as missing one day will be less detrimental.