Making sure designs are user friendly relies on using the right information.
The right information must also be interpreted, and used in the right way. This is where an Ergonomist can help. Understand how humans use spaces, expect things to work and interact with their environment helps inform designs.
To decide how wide a space should be or the height of a bench top, requires an understanding of what the space is used for, the surrounding environment, and importantly the requirements, capabilities and expectations of the users.
Additionally, knowing which aspects of the workplace need this kind of consideration is difficult to determine. Getting the right information from your client, performing potential hazard identification, and risk assessments all contribute to making sure you have all the information you need to design a workplace that will not only be safe, but provide the users with a space that compliments they way they work. That is good design.