I'm sure most people have heard about the horrors of sphagnum moss causing root rot. I have previously used medium/coarse bark mix as a universal medium for all of my orchids. I live in a particularly arid climate (humidity is usually ~40%). My orchids have never "thrived" under my care. I unpotted an orchid one day to look at the roots and confirmed that it was under watered. As an experiment, I repotted some of my orchids in a sphagnum moss/bark mix and have experienced crazy growth. I have now repotted my entire collection in a sphagnum moss/bark mix. The smaller orchids have a higher sphagnum moss to bark ratio while the larger orchids have a lower sphagnum moss to bark ratio. The pseudobulbs of my oncidiums have remained plump and my other orchids are putting out lots of roots. My point is sphagnum moss is not as bad as everyone makes it out to be. It works great for under waterers in arid climates. I understand that what works for me may not work for other people, but I just wanted to share my experiences with sphagnum moss.
Edit: Also, I find it easier to tell when to water my orchids when planted in a sphagnum moss/bark mix. Since the mix tends to dry out more evenly than a pure fir bark mix, I can simply look at the surface of the medium to determine if the orchid needs to be watered.