Boxers know it. The heavy bag is a great training tool.
Unfortunately I do not have a true heavy bag at home because I don’t have a means for mounting one. However, I do have a Wavemaster XXL, which is better than nothing.
I use the bag every so often in my workouts because striking something gives far more feedback than just “air striking”. But the past couple weeks I’ve been almost exclusively focusing on bag training in my at-home workouts. It’s been quite a workout too, and a welcome bit of variety.
The heavy bag isn’t just about working on your striking, but it can also help with your footwork and even defensive skills. This is where the floor-mounted bag like the Wavemaster is at a disadvantage, since the swinging of a true heavy bag is really needed to work these. Nevertheless, I still try to keep moving and do the best I can with what I have.
Check out rossboxing.com’s heavy bag training routines. Doing 3 x 3-minute rounds of skills, 4 x 1-minute rounds of power, followed by 5 x 30-seconds of speed is just killer. Another routine from Ross.
An overview/intro to bag workouts from bodybuilding.com.
Work the bag into your workout routine. If nothing else, sometimes hitting something is just great stress relief. 🙂
Stuff From Hsoi 
Not only do heavy bags provide feedback and more accurate training, it’s been found that kicking the air can have a negative impact on your knees and other joints.
Ah yes, very good point. You can “snap” your hand/foot out there and what stops it? Well, that your skeletal structure doesn’t extend any further… that’s what stops it. But consequently your elbow/knee joint ends up absorbing a lot of that force/momentum.
Good point. Thank you for adding it.