It's a strange thing to do, but if they are using the correct lane and pull back in when they have overtaken, I can't really see how it causes anyone any inconvenience ?
It's usually a symptom of them not concentrating fully.
Drive along at (eg) 70mph, adjust satnav, speed drops to 55.
Increase speed to 70 again, take a drink of coffee, speed drops to 55.
Just forces other traffic to change lane around them, which while not the end of the world, increases stress and the chance of an accident.
The issue with pulling back in between lorries is this
Agreed.
The other issue is that [i]if you actually care about maintaining proper stopping distances[/i] (rare) then you need a fairly large gap between the vehicles to make it worthwhile pulling in.
e.g. if you try to stick to [i]"only a fool breaks the 2-second rule"[/i] at 70mph then you shouldn't be closer than ~205ft (62m) to the vehicle in front.
So if you intend to pull in between two vehicles you'd want to be 205ft in front of the first one with another 205ft in front of you till the second - PLUS whatever distance you'll cover in the speed differential between you and the vehicle in front while folk overtake you.
That's quite a big distance - and results in people driving up behind you and complaining you are "hogging" the middle lane by not pulling in when it is "clear".
