Originally Posted by
skyplane
They will only do this when the flights are very busy and full. This to avoid lack of space in the overhead bins and to improve the ontime departures.
That's my impression as well. Note though that I ve never had my bag weighed --or for that matter observed anybody having their bag weighed-- during priority boarding (so either Plus pax or Go pax with *G) at LHR, even on full flights. But my luggage is always well within the size, and most of the times weight limit, I guess this helps as well. I suppose that if I showed up with a clearly oversize/overweight bag that could draw attention...