I built an 'Urban Mountain Bike' and I sometimes like to take it off drops. Accordingly, I cut the 'nub' that sticks up above the top tube so that the seat can be removed without a scary open pipe ...
I recently moved, and had to take off the seat to my bike while I moved. I was surprised to find when I arrived and settled that I couldn't find the clamp to my bike seat. I managed to find a new bike ...