The USGA had three main reasons for introducing the rule:
Prior to that rule golfers were allowed to bring as many clubs as they liked. A field survey at the 1935 US Open and Amateur found that the average number of clubs carried by a single player that day was 18. It simply became too much for the caddies.
The highest total number of 35 clubs, a player carried, was recorded in 1935. He had a full set of left- and right-handed clubs in the same bag. His feeling was, ‘If my ball comes to rest against a tree, why should I be disadvantaged?’ It was around this time everyone decided things were out of control.”
Official rule at: www.randa.org