When do you start sending you kids on trips (without you)?

I see the question about at what age parents are ok traveling without their kids, but when are other people sending their kids alone on trips without them? Like vacation with friends or family? A sporting event over a weekend? Things like that.

I don't have unlimited PTO and despite my best efforts, not a great network nearby. What my kids do have, is the ability to travel with family and close friends, but without me. What criteria help you decide when they're ready? Do you feel bad sending them and not coming along?