I never felt like I was "shipping" anyone off, and I find that a little insulting.
Preschool was loads of fun for my kids. They made friends, they did crafts, they learned about different cultures and music and art and animals. My dd knew more about the Impressionists at age 5 than I do as an adult, and that knowledge and love of art history has stayed with her. They have great memories of preschool, and go visit their old teachers every couple years.
Of course it wasn't necessary, and I'm sure they'd be perfectly fine if they hadn't gone. But I believe it enriched their lives, and I'd do it again in a heartbeat.