HIIT workouts are High Intensity Interval Training workouts. That is where you do short, intense bouts of work with brief recovery between.
These are beneficial for many reasons:
1). Getting the heart rate up, working on your cardiovascular health.
2). Lung capacity increases. These workouts make you breathe harder, even slightly out of breath, so the lungs fill to capacity and get stronger.
3). Memory health. Working out in general helps the memory, but especially the high intensity and memorization of what exercise is to come next.
4). Reverse muscular decline. HIIT workouts build muscular strength even when resistance equipment is not used. Bodyweight and quick moves helps muscles and endurance.
These are just a few great reasons to include interval training into your normal routines. Even during a walk, pick up the pace then bring it back down to a normal pace. Do that a few times, then increase as it becomes comfortable and easier.
Aim for 1-2x a week, as these workouts are taxing on the body. But beneficial to add to your normal routine.
Stay happy and healthy and positive always!