Originally Posted by James Howard
Technically, for a turn up and go user, the time will be worse. At 15 minute frequency, the average wait time is 7.5 minutes. So you'll gain 2.5 minutes from frequency but lose 3 minutes in journey time
People making short journeys (i.e. Dart passengers) tend not to think about it that way. Wait time is more of a consideration than journey time, especially for ad-hoc passengers.
Dart has a bad reputation for being infrequent and having silly, unpredictable gaps between trains. They've been working on it for the last few years but it'll take time to lose that image. A 10 minute gap goes a long way towards achieving that (notwithstanding the negative impact on other services).