Off the top of my head.
CSEs may provide better analgesia even after the intrathecal dose is gone. Cappiello 2008 in A&A published an article about dural puncture epidurals showing generally better results compared to plain epidurals. I don't really buy all the conclusions, but there's some good foot for thought in the article.
What I like best about CSEs, other than the patient's instant gratification, is that you can safely start the pump and walk away from the patient. An opiate-tilted intrathecal dose won't cause hypotension. You can chop an easy 10 minutes off the whole encounter by not having to stick around to bolus the epidural.
PCAs for labor are fundamentally different than PCAs for every other purpose. You need a fast onset drug, and there needs to be minimum lag time between button hit and drug in bloodstream - this means a Y at the angiocath, with a briskly moving carrier fluid in one arm and the drug in the other. The usual PCA setup with the drug going into an IV port 12" away from the patient isn't going to work. I favor remifentanil with a .02 mcg/kg/min basal and and 0.2 mcg/kg bolus with a 1 min lockout, and you have to sit there and sit there and sit there and adjust until it's tuned right. It's a PITA but it works for people who can't get epidurals.