I think every resident should moonlight after 2.5 years of residency (with PD's being in charge of who is allowed to moonlight). There is no reason a REsident should not moonlight the last 2 months of their Residency. I went to a great residency in NC, but my experience was made exponentially better by moonlighting. I moonlit at a tiny, garbage county hospital, and that's where I really learned to be an emergency physician. By the time I started my first attending job, I didn't skip a beat due to my experience moonlighting
You don't know what you don't know, till you do it on your own. The reason so many people quit their first jobs in ED is b/c they don't have eyes open on just how hard and stressful it can be on the outside. Believe it or not, Residency, no matter how good, cannot replicate the lack of safety net you have once you become an attending. Also, most hospitals don't have every specialty at your beckon call, as residencies do. I worked at a dinky county hospital where I saw some of the sickest patients who walked in. I had a surgeon and a hospitalist. No ICU. No anesthesia, no Cards. No ortho. I had to transfer every patient requiring cards/ICU/specialist. If you can make it there, you can make it any where.
I can tell you hiring in hiring Residents in a community hospital, moonlighting trumps anything else as a positive. You were published in NEJM--good for you. Fellowship--great! You went to House of God Residency--cool! Now can you run an ER with 12 beds filled, 6 more in the waiting room while trying to transfer an intubated patient? That's the doctor you want working at your group (obviously academics is another beast, but most residents don't go on to work academics). Outside of liability or lifestyle, there is no reason why a resident in their last 2 months cannot moonlight (and the liability will be there the second you get out, so best to learn to live with it).
As for screwing our specialty--the other doctors at that county hospital were FP's or moonlighting from other specialties. There are more jobs than EP's in this country (who here doesn't get 5 job offers emailed daily as spam?) Some were solid but many were complete duds. As above, I would rather have a 2.5 EM resident caring for my family than a FP on his 5th different job moonlighting at a hospital he's been to twice. If a program doesn't let you moonlight, they are doing you a disservice. Plus, the $ doesn't hurt either.