To put your comment into the 'bigger picture', as I see it at least: if I can assume that by efficiency, you mean the rate of verbal exchange of information, then I would argue that this is often not the sole function of a conversation; for example, building rapport is often an indirect but desirable outcome. There are no doubt other outcomes and that they vary wildly by context. Though to stick with rapport: pursuing near-optimal information exchange through interruptions may (and for anti-interrupt people, probably will) come at the hefty cost of rapport which may effect future conversations.

This is a super interesting topic and also cool because everyone has a slightly different take. I had not really considered that people who interrupt may do so because they actually like it and think it's beneficial. I just (probably prematurely) assumed it was a bit of a personal flaw based on how it made me feel.