Due to the solid mahogany body of a Gibson Les Paul model and the shortage of lighter mahogany in the early 1980’s Gibson started using Weight Relief. This consisted of drilling 9 holes through the body in the so called “swiss cheese” format.
This continued until around 2007 and was used after that on the Traditional models although some are available from 2013 without any weight relief. (Lighter wood?)
Before this Les Paul guitars were getting heavier especially the Custom models as these were a one piece solid body. Over 40% heavier in some cases.
As the available mahogany got heavier Gibson switched to Chambering which helped a lot with the weight.
Only specific models were chambered before 2007.
Recently Gibson announced Modern Weight Relief which is a little different here is the link: