The two ways I think you can mainly use the number three for are the safety of the back and the stability of the feet.
Three points in the back
The lumbar spine / buttocks, shoulder blades and back of the head should go in a straight line if you use a broomstick (the one you already used in your home training if you followed the blog and the challenges, read more about it in for example Improve exercise at home with household utensils). If you find that line, your lifts (for example deadlifts and squats) will be safer for your back and your body will focus the energy in the right place.
If you find your three points in the back, you also have a good tool for checking your mobility and stability when you do a deep squat (for squatting) with a barbell over your head. Do you have the three points (lumbar / buttocks, shoulder blades and back in line while the arms are locked and in line with or just behind the ears, I think (note that here are different schools around the world) that you have found the right position.
Three points in the foot
The heel, big toe and outer part of the pad (or all toes). If you have the three points in the floor, you have a good balance in the foot, something that will spread in the form of good angles to the legs, up through the hip so that the muscles and other parts of the musculoskeletal system can work with anatomically correct angles. Of course, there are exceptions here, although what I describe is what I believe is right for sustainable health and good results.
Find your three points and you will get a sustainable health and improved results.
Please give me your thoughts below, I am always open for comments!