In EN 61340-5-1:2001 the user guide suggests that parts of the standard need not be adopted if they are not relevant or needed for the processes carried out. In practice this is open to interpretation. In an electronics facility, is the use of ESD garments really necessary?
I interpret the standard as clearly saying that if you use ESD garments then they must conform to the standard. The more difficult question is, are they necessary and appropriate in your particular case? This is a very hard one to argue and in the end it often boils down to a personal judgement based on your view of your product and processes.
At one extreme if you were making a cheap "throw away" consumer product with cheap components that were not particularly ESD susceptible then I think you might not worry about using ESD garments. At the other extreme if you have a high reliability product with high cost of failure (e.g. satellite) using high susceptibility components then you would clearly take more care and use ESD garments. Most facilities operate somewhere in between.
As another consideration, if your operators all wear cotton tee shirts in a tropical climate there is likely to be little ESD risk. If they may wear long sleeved fleeces or woolly jumpers there may well be some risk from charged clothing and use of ESD garments may be advisable. Another consideration is that use of ESD garments helps to enforce ESD discipline and keep people in the right frame of mind that they should be ESD aware while wearing the coat.