Therefore class type 100 is used but if needed class type 017 is of interest as well (e.g. if you handle imported documents in CG50/C54).
The benefit of using the Classification system is clear. By some customizing etc. activities you can easily enlarge the property tree if needed or you can specify your own trees. An important part here is that you can use "phrase management" in context of definition of the characteristic. Therefore on high level these types of characteristics are used in EHS very often:
Phrase based characteristics (with one and / or more values allowed)
Numeric based characteristics (with or without Unit Of Measurement)
Regulatory List driven characteristics
With higher SAP releases more customizing activities are needed to prepare a new value assignment type/property. What is important to understand: the classification system of SAP is "master data". But in EHS this is combined with other customizing activities and you need to execute an import/export of property tree to prepare new value assignment types. As well the implementation of new SAP classes is difficult (a lot of problems can come up).
Issues with value assignment types etc. have been discussed often here. The following list tries to give an overview (list will be sorted later). This list should provide the "FAQ" for use of classification system in EHS.