I travel by plane on average 3-4 times per month, mainly in Europe. One thing I have noticed is that despite the advantages offered by electronic passport gates, on almost every occasion and at almost every airport I have visited, a significant number of the machines (often around half) are out of use and displaying a red X. In many cases this is in spite of the fact that there are huge queues both at the electronic gates and the manned gates.
Why is this the case? These machines are fully automated, and passengers who are unable to successfully get through them are diverted to a manned gate anyway, so it is hard to see how it could be related to a staffing issue. I also find it hard to believe that it could be due to faults - surely the machines are not that unreliable, and typically the ones that are out of use are all in a row.
If there is some legitimate reason, then why install more gates than are going to be used in practice?