Any exercise is better than no exercise...for the most part (image source)
A recent study determined that closed chain exercises are better than open chain exercises at increasing Bone Mineral Density (BMD) and decreasing fall risk.
"The strongest effect on BMD and fall risk was recorded by the closed kinetic chain exercise...Osteoporotic postmenopausal women should be prescribed closed kinetic chain exercise to diminish the effects of the disease and minimise their risk of fall."
Don't Do This
This exercise may have it's place in certain situations.
But the open chain aspect (foot not connected to the ground) makes it ineffective for increasing bone mineral density.
Do This Instead
Closed chain exercises, like the one above, are much better for BMD.
An even better option is performing squats (below).
Summary
Adding closed chain exercises will help to decrease fall risk and improve BMD. It's an easy task to significantly improve one's health.
If you're not sure what exercises to perform, seek out a good physical therapist or personal trainer.