Stretching any major muscles in your body will always promote healthy blood flow and fluid exchange, which keep your muscles well nourished and relatively free of buildup of waste products, which lead to optimal function and lower risk of injury.
However stretching your hamstrings will likely be where you get greatest overall return on your health. Originating from your pelvis, spanning the length of your thighs, and inserting into your lower legs, your hamstrings directly affect two of the most important weight-bearing joints in your body – your hips and your knees.
If your hamstrings are tight, which to be fair they are on most of us, they will create a downward pull of the pelvis, which causes strain and pain in hips and lower back.
As the pelvis gets pulled down the lower back flatten out and we loose the natural curve that is meant to stabilize us. With the pelvis limited motion here the lower back usually have to do more movement than it is meant to, for us to still be able to go about our daily life, putting even more pressure on it
Tight hamstrings can also change the way your knee moves, which over time will grind away cartilage quicker than your body can replace it.
So spending some love on your hamstrings is always worth it as it will improve posture, back ache, general movement and blood flow through your entire body.