Sometimes I an appreciate wanting to cruise in the middle lane, because ADAS level 2 systems common on cars today is far more comfortable when it does not have to deal with regular merging traffic. But aside from that, I really don't like it when people camp in the middle lane because they tend to form a pretty tight line and manage to effectively turn a three-lane highway into two single-lane highways -- hard to get through from one side to the other.
Sorry, I didn't fully explain the idiom: "centre lane" refers to the right-most (what in the US would be left-most) "fast" lane - the one closest to the centre of the highway as a whole.
To your point, I think the middle lane of a three-lane road is, ideally, the correct travel lane. Cruising there at the prevailing speed leaves one lane more lightly traveled for entering and exiting, and the other for passing. Predominantly using that lane minimizes lane changes, which are the most dangerous driving moments. You're right, though, that the strategy breaks down as traffic gets heavier, and gets ruined entirely when (as under discussion in this thread) people gum up the supposed "fast lane".
A custom that (where I live) is becoming more honored in the breach than the observance. It makes driving very much more dangerous.
In Britain they have a sardonic nickname for people who do this: CLARAs. "Centre Lane Residency Association".