Like many of the older or more experienced guys, I have done it too in the past.
Most of these windows, if they were the sash type could be done by "sitting out"
You sat on the outside ledge and pulled the window down to your knees. You could then pull the top section down and push the bottom section up, and then you could do the bit you had missed.
With windows that were too tall for this, standing on the sill was the only way you could do it. Doing the bottom panes was the hard bit.
I once worked on a Llandudno hotel that had a nine inch ledge about a couple of feet below the sills. I was 17 at the time, working with an older guy.
When he finished his window he wanted to pass me to get to the next. As I said this ledge was only 9 inches wide, and the only way he could pass me was to hold on to my waist and swing round the outside of me. I was terrified, hanging onto the window frame by my finger tips and having to bare this guys weight as he sqeezed passed.
Now I have no time for lies or liars, what I have told you is the gospel truth.
These practices were common place and you, as a youngster were mocked by your peers if you showed any fear.
The guy who squeezed past me, 4 years later, lay down in front of a train. He died leaving a wife and 8 children.
This took place back in 1959, but the practice still goes on to this day.
I wouldn't do it now, but I have in the past. Dai