Well, all cells convert oxygen and sugar into energy, including old cells and cancer cells. Like you said, cellular senescence is a trade-off -- the body doesn

Well, all cells convert oxygen and sugar into energy, including old cells and cancer cells. Like you said, cellular senescence is a trade-off -- the body doesn't want these damaged cells to keep dividing per se, yet they are still useful for continuing to covert sugar and oxygen into energy to use as needed. We do have a mechanism for getting rid of damaged cells in general: autophagy. However, autophagy seems to be mostly triggered when there is an energy deficit, for instance during fasting or during intense exercise. This is probably why fasting and exercise are proven over and over to be beneficial to health, they essentially trigger a "cleaning cycle" of cellular autophagy within the body. I'm not sure autophagy typically includes senescent cells, my understanding is that it's primarily targeted towards cells that have damaged mitochondria.