Most of the circulated "horse blanket" notes have creases from being folded lengthwise. This was due to the use of money belts. Storing them folded this way allowed the owners to thumb through the notes to find the denomination they wanted. Rich
The introduction of smaller sized currency notes in 1929 was the culmination of a 20 years effort to achieve that goal. Franklin MacVeagh, who served as Secretary of the Treasury under President Taft from 1909 to 1913, can be credited with fathering the idea. Banks often printed advertisement/informative leaflets to help the public with the change. They made the leaflets the same size as the new smaller currency. Pardon the pun, but it was a big deal when it happened.
Could a reason also be that people did not trust in the value of paper? Back in the good old days everybody knew that gold and silver would get them where they wanted to go, but paper money was a crapshoot. Especially with all the banks going broke left and right, a small bill would (perhaps) make people feel that it was small value. Making bills huge could have been an attempt to reassure people in the value of paper.