I've bought a punching bag to one of my kids when she was 2 years old. It was the best spent money ever since my wife's wedding ring.
The thing is dangling from the ceiling of her room. She is free to kick, tackle, punch, hug, climb, and do whatever she wants with it. It's a little center of extreme activity for her inside the house, which is perfect for a very active kid like her. It's perfect to keep her busy when she can't go outside for some reason, like rainy days.
Punching that thing is a excellent and fun way for her to blow off some energy and is way better than letting her play with a tablet or some other device like that.
Just be careful with the space around the punching bag - be sure it's open and put some sort of soft material on the floor beneath it, in the case your kid falls down while playing with it.
The only con I can think of is that playing fight with your kid will start to hurt you a lot more.