Stepping on the scale and seeing that nothing has changed can be frustrating for our patients.

They and we (health professionals) want them to achieve their goals. However, weight should not be the focus, as there are healthy overweight patients, while others with "normal body weight" have changes in their biochemical exams, for example.

A body composition allows assessing what your weight really comprises: whether more muscle mass or more body fat. The difference between the percentage of these tissues makes the metabolism work for or against us.  The greater the lean muscle mass, the less body fat - which can lead to higher (but healthier) body weight.

Therefore, bodyweight alone cannot determine what the real condition of everyone is, and more importantly, it can lead to some misconceptions about the individual's health status. Thus, the assessment of body composition makes a huge difference when guiding the patient towards a better quality of life.

 
Reference:

Bacon L, Aphramor L. Weight science: evaluating the evidence for a paradigm shift. Nutr J. 2011 Jan 24;10:9. doi: 10.1186/1475-2891-10-9. Erratum in: Nutr J. 2011;10:69. PMID: 21261939; PMCID: PMC3041737.