I think body weight is essential for overall fitness (if you can do a bodyweight squat it will help you perform squats with weights)..
BUT (to quote Simon Cowell) having said that…many people cannot perform body weight exercises (consider people who can’t perform push ups or have trouble with a body weight squat).
A nice plan of action is to work on the strength and stability necessary for body weight activity. Resistance machines and planks are two ways to improve strength and stability (respectively). *
Once a person improves in these 2 areas a trainer can consider how to improve their body weight exercises.
The trainer should be able to determine..
1) the client’s ability to perform body weight exercises
2) how to improve the client’s ability to perform body weight exercises
3) how to incorporate bodyweight exercise with weight loaded exercise
Good luck with your clients!
* These are examples; they are not the only ways to improve these areas!