Coupled with Modern Society, it Would Increase Life Expectancy
When you look at Willk's answer, you see that the 2 leading causes of death are by far heart disease and cancer with heart disease exceeding all forms of cancer combined. It is true that the heart is the 3rd most resistant organ in the human body to cancer; so, making it regenerative would increase the rate of heart cancer pushing the cancer death rate up a notch ... but this could also massively reduce deaths from heart disease. While cholesterol buildup is often blamed for pulmonary illness, various studies over the past couple decades suggest that this is probably a symptom, not a cause. When an artery becomes weakened or damaged, our bodies coat our arteries with cholesterol on purpose to reinforce and protect it, but our heart and arteries have limited actual healing capabilities due to poor regeneration. If the pulmonary system could better heal itself, then our bodies would not need to respond with cholesterol buildup which means that heart disease as we know it could be all but eliminated. So, you could trade a lot of prevented heart disease for a little bit of heart cancer.
Then you look at the next 3 lowest things: Accidents, Chronic Lower Respiratory, & Stroke. Many accidents cause chronic, unrecoverable injuries. With our current bodies, most major accidents end not with instant death, but being put on various types of life support and waiting to see if the body can heal itself. Many people who go onto life support never recover, but with better regeneration, life-support would become far more successful at saving lives and allowing a person to return to full health. Chronic Lower Respiratory diseases are normally caused by scaring of the lower lungs from smoking or major infections. With better regeneration, your lungs could fully heal following these events making later life respiratory issues far less common. Strokes would also not necessarily become less common, but making full recoveries would become more common.
But the biggest life saver of all here is improved quality of life. People who are not in chronic pain live happier lives. Of all health factors that determine how long you will live, happiness is probably the most important due to its direct relationship with pulmonary heath and your immune system, and better regeneration helps you maintain better happiness as you age.
So what does this all have to do with Modern Society?
Human biology is designed to optimize our survival to how our ancestors lived.
Our medial pulmonary systems don't regenerate very well because physically active humans living off of a natural diet can live a very long time as is; so, no need for better regeneration there. But now that we are living longer and eating worse, a regenerative heart would become more practical. Modern medical interventions also mean that we are MUCH better at stopping a simple wound from killing you quickly. If getting a leg cut off is rapidly fatal to pre-modern man, then there is no reason to care if your body has a long-term plan for recovery, but if you can consistently stop the fast death, then better regeneration helps prevent slow death.
We are also a lot better now at treating cancer than our ancestors were. To premodern man, cancer was an absolute death sentence; so, our biology tries to avoid it by reducing cell divisions to minimal requirements. But with modern medicine, we can cut it out, irradiate it, chemo it, etc. Ironically, better regeneration may actually decrease the chance of dyeing of cancer despite higher cancer rates because more invasive treatment options would open up.
So, if you went back to 50,000BCE and made humans super regenerative, it would not be very beneficial, but do it today, I am pretty sure it would help a lot.