‘Type and frequency’ is something of a mantra in the Vanguard Method.
To design a service you need to understand the type and frequency of (value) demand.
When you study a service you want to know the type and frequency of failure demand.
When you study a service you often want to understand the type and frequency of failure to provide the service the customer wanted (e.g. failure to resolve at first point of transaction, failure to fix first time).
When you are studying a flow and things go to different places, you’ll want to know which types go which ways and how often.
When you are studying a flow and things go wrong you’ll want to know the type and frequency of problems/errors/faults etc.
And the key to good knowledge is predictability.
Conventional managers assume nothing is predictable; they are often surprised to learn how predictable things are when they study their system.