Evoko Liso uses impersonation as it has many key advantages over delegation which the predecessor Evoko Room Manager uses.
With delegation, each connection made to EWS (Exchange Web Services) is done by a specific account with delegation. This is no problem with smaller installation as the default EWSMaxConcurrency value will allow up to 10 concurrent connections to Office 365. But for larger installations, this requires a lot of service accounts to avoid the risk of throttling communication.
For example, using Office365 where the limit is fixed to only 10 you would need to setup +50 service accounts if you have 500 rooms.
With the Evoko Liso we are aiming for a much more “real time” experience in which such throttling policies could become an even bigger problem.
With impersonation, only a single service account (e.g. email@example.com) is used for all communication, but in the “eyes” of Exchange server it is the individual rooms that makes the connection and therefore there are no issues with EWSMaxConcurrency, EWSMaxSubscriptions or any other throttling policy that could cause unwanted behavior.