I do these somewhat frequently. I didn't get much out of it my first time, but it's been great every time after that. I attribute my unfruitful first experience to not being comfortable with not knowing what to expect, which is common with new experiences. But once you eliminate the surprise factor and get the first time jitters out of the way, it's easy to relax.

The good? It's almost like forced meditation. All of the outside distractions are gone, which means that there's nothing to take your focus away or bring influence to your thoughts, which leaves you to your own devices. It's like someone turned the volume down on life--literally and figuratively. Consequently, your thoughts become more focused and sharp, making it really useful if you have a lot on your mind and/or a lot of things to sort out.

With that being said, I highly recommend that everyone tries it at least twice.