I started SS 6 months before full retirement age because I retired 4 months before it and I wanted SS to start first to put a little cash cushion into my bank account. I was only going to start SS one month before I retired but a chipper young person called me from SS to caution me that the payment arrives the month after and so did I want to start one month before the date I'd put on the form. I actually had known that and did want to really start on the date I'd filled in, but, I didn't want to demoralize the person since she'd made the effort to call me, so I pretended to be happy to get the info and to yes start my SS a month sooner.
I remember trying to decide when to start and running the numbers and while I would regret the amount I was giving up (don't remember now, might have been 8k less for the expected lifespan), it wasn't significant enough to want to work longer. I wish I'd retired earlier and started SS earlier, but it wasn't financially feasible since I didn't get serious about saving for retirement until the last years of my working career.
If I'd had enough money to both retire and also delay taking SS, then I guess it would make sense to delay to age 70. My brother delayed his to the latest possible time. I think that is mostly a luxury for well-off people, tho I guess it would be useful for someone who didn't mind working until age 70, or sadly for people who have to work until 70.