Process platforms are used unevenly. The service desk lives in the system all day. The head of department approves an order twice a week; a technician on the shop floor reports a defect once a month. Counting named users treats all three the same, as if each of them had a full-time seat.
Concurrent licensing reflects how work actually happens. What counts is the number of sessions active at the same time. Twenty approvers who each spend a few minutes in the system over the course of the day do not take up twenty licences.
This matters beyond price: you can bring everyone involved in a process into the system. Nobody has to collect an approval by email because someone was spared a login. That is often where gaps in a process appear.