Creating lag in the golf swing leads to a more compressed strike. Compressing the golf ball allows you to hit it further and have a more controlled flight, particularly in windy conditions. Please see photo attached of what Lag in the golf swing looks like. It’s pretty self explanatory as the club head is able to lag behind the hands as the hands reach level with the ball. In other words the hands get to the ball before the club head. Creating lag is done by one of two ways, firstly forward leaning of the shaft at set up and impact, and also by hitting down on the ball which allows you to compress the ball down.
Imagine you start your downswing slowly leading with your body and hands, feel like the hips are creating a downward force towards the ground. Imagine keeping your wrists soft, this feel will help you create lag. In the picture provided of Lucas Herbert you can see the angle created between the left arm and and the club shaft (vice versa for left handed golfer). When you achieve lag in the golf swing, the club will naturally shallow at the bottom of the arc of the swing, that’s how you know you’ve achieved real lag. As you can see in the photo this the type of angle you are trying to create.