Originally Posted by dddd

Some bikes, like the Schwinn Varsity and Continental, have particularly high bottom brackets, which is compounded by slack frame geometry that reduces the frame's forward reach by several centimeters. The rider thus my prefer the reach of a larger frame size, but then have problems with the standover height. This unusual instance begs for the use of small-diameter wheels (to the extent that 4mm matters).

Another consideration is the leverage of the braking system. A 4mm smaller-radius rim will reduce the leverage on a bike with caliper brakes, but will increase the leverage on a bike with cantilever brakes. This difference is noticeable, as the 4mm is around 10% of the arm length in many cases (the vertical distance from the pivot to the rim).

A 27" wheeled bike may look different and have a lower bb (and thus balance differently on a kickstand) with smaller-diameter wheels unless the tires are made plumper to restore the OD of the 700c tire.