FRL (Filter, Regulator, Lubricator) units are essential components in compressed air systems, designed to ensure clean, regulated, and lubricated air supply. However, their use is not universally applicable to all types of compressed air systems. 
FRL units are most suitable for pneumatic systems where lubrication is necessary for the operation of air tools and equipment. The lubricator component introduces a controlled amount of oil into the air stream, which is essential for the longevity and efficiency of certain pneumatic devices. However, not all compressed air systems require or can accommodate lubrication. 
For instance, in systems where the air is used for breathing, painting, or in food and pharmaceutical industries, oil contamination is undesirable. In such cases, using an FRL with a lubricator would be inappropriate, and only the filter and regulator components might be used. Additionally, some modern pneumatic tools are designed to be oil-free, eliminating the need for lubrication.
Moreover, the compatibility of an FRL unit with a specific compressed air system depends on factors such as the system's pressure requirements, flow rate, and the type of equipment being used. The materials used in the construction of the FRL unit must also be compatible with the air quality and environmental conditions of the system.
In summary, while FRL units are versatile and beneficial for many compressed air systems, they are not universally applicable. The decision to use an FRL, particularly the lubricator component, should be based on the specific requirements and constraints of the system in question.