I never found that the exit forms caused any lost time.
As far as I could see no one actually took the slightest notice of them.
i have always wondered a bit why they are so cautious about people leaving the country.
Yes. I often wondered why they cared. Do you think there was an office somewhere where some poor soul had to match all the incoming forms with the bit you give to security so you can leave the airport with the exit forms? Wouldn't surprise me!
Flying in from Manchester last season (March) we filled the usual ones in on the plane, on arriving at the new terminal these were taken off us, and one that was half size handed out (still had to put same info on). When we checked in for departure I couldn't find any and when I quizzed an official, was told they were no longer required.