I have seen a lot of weightlifters and especially rugby players tie some weights after them most of the times a sled and pulling it at full speed for a distance,I understand it could make a rugby player get used pushing high weights because he needs to push other players in games but does in help in any other way?
Well, ask yourself this; how does it benefit a rugby player?
Muscles are multi-purpose. Even if you train the muscles in one particular way, the muscles will be able to perform other movements too.
Take bench press. When will you ever need the ability to lay on a completely flat surface, and press a completely symmetrical and balanced object up and down?
Never. But you train the chest and triceps, and these muscles are used for all kinds of pressing movements.
Now, consider the same concept, but with the muscles trained by dragging weights.
It's what we call a functional exercise. It's a type of movement that mimics things we might need to do in daily life, and also, it covers so many muscle groups at the same time, that you get a LOT of training done with every set.
When an exercise covers so many parts of the body, it not only builds a lot of muscle, but helps with developing balance, endurance, and the central nervous system.