Anytime bodyweight is mentioned in the realm of sports training, images of "functional training" and weak, overly flexible athletes dance in our heads. So the industry has chosen to base intensities in training off more thundering concepts like maximum speed or the 1 repetition max (1 RM) of a lift. These maximum bases are less reliable than bodyweight because they cannot be measured as often and fluctuate daily based on a host of variables. Then the problem is further complicated as conjured algorithms try to solve the problem by "estimating" maximum performances to base training around.
As a former Olympic lifter myself, and having close friends who hold world and domestic powerlifting records, estimated maximum values do NOT equate to real maximum performances. Whether it is a maximum speed or weighted movement, these actions cannot be done frequently in a population that plays a sport; athletes are not lifters, and not exclusively sprinters either so we need to find better ways.
Body Weight; Reliable, Sensitive, Valid
Body weight is the most reliable and practical metric for intensity available. You can measure bodyweight daily and using the same weighing device, the values will be relatively consistent. Furthermore, we must remember that most athletes are not lifters so their lifting performance change just by improving skill alone. They get more efficient at the specific skill, due to practice and good coaching!
Bodyweight also has a holistic correlation with every physiological process, making it incredibly sensitive to a spectrum of stimuli. Without invasion of privacy, we can often suspect our females' menstrual cycles when we see a 3-4 pound increase, likely due to an increase in water retention. Poor weekend care (less sleep, water, and food) leads to athletes showing up with significantly lower bodyweight than the week before.
But we are still left with this poor image of squatting or training intensively off bodyweight rather than a more impressive number. So we need to think abstractly; training off bodyweight %s does not end at 100% of bodyweight. Athletes can be prescribed intensities for their lifts that are far in excess of their own bodyweight, particularly in the larger movements like squat, deadlift, and split squat. For example, our goals for deadlift in level 2 (an intermediate measure of training age) is 130% of bodyweight for 3 sets of 3.
This validity of using bodyweight to measure training improvements is further strengthened by the athlete's relative speed or strength. As they get larger, their requirements for strength must improve as well, otherwise we just created non-functional mass...useless force. This provision is helpful for both male and female athletes as it simplifies the collection of a host of body weight metrics; absolute weight, body fat %, lean mass, etc. The goal is just so simple in an era where there is too much data, too many graphs/charts...just get strong. Your ideal body fat and body weight is whatever allows you to produce more relative force.
1RM's and estimated 1RM's are unreliable and impractical
%Bodyweight is reliable, and sensitive to an athlete's changes/habits
%Bodyweight is valid. As athletes, if you want to get larger, it is so you can produce more force. If you can't produce more force with the gain, then you created non-functional mass. Using %BW as a loadbase regulates this need to produce more force when there is a gain in weight.