When you read the FA-blogs you notice that there's a lot of talk about exercising according to the principles of HAES (Health at Every Size). One of the leading HAES-gurus and fitness-instructors is Kelly Bliss (www.kellybliss.com).
The basic idea is that the primary goal of exercise should be health and not weight-loss, and that you can enjoy exercise regardless of your size. This all sounds wonderful to me, good health and not appearance should be the ultimate goal for any exercise-regime, and your size should never prevent you from working out. I'm all for this philosophy - but after checking out Kelly Bliss' homepage I still have a huge problem with HAES.
For exercise to improve your health you need to challenge your body. It goes without saying that the intensity that is needed depends on how fit you are. For someone who weighs 250 pounds and is new to exercise a 10 min walk or similar can be more than enough of a challenge, but for someone who has some 30-40 pounds extra and is used to walking, a gym-session with some jogging or other cardio, plus some resistance-training, that works up a good sweat is a good beginner-level challenge.
IMO a good rough thumb-rule is that at beginner-level you should sweat and feel some discomfort for some 20-30 mins for a work-out to be beneficial.
The idea is that when you get into an exercise regime your fitness improves, and you gradually have to do more to keep challenging your body and get continued health-benefits.
It's up to the individual what level of fitness you think is enough for you, ie when you think that you are in so good a shape that you don't concentrate on continuous improvement, but just on maintaining the level that you have achieved.
Kelly Bliss' HAES-videos are, IMO, just not challenging enough for significant health-improvement, unless you are so severely overweight that you are disabled by your weight. And even in that case the goal ought to be to use exercise as a tool to lose the weight (ie remove the disabling factor), and gradually move on to more challenging work-outs.
At best HAES could serve as an introduction to exercise, but at worst it will have you stuck at a very basic level and give you a false belief that you exercise regularily and are in good health.