Cyle, I think on a hardtail, you're fine with a narrow/wide ring and a clutch rear derailleur. My feeling is that some dual suspension bikes that put slack in the chain when the suspension moves through the travel can still throw the chain.
For instance, Santa Cruz was specing the Bronson with SRAMs XX1 group and a chain guide at least for a while.
I run a chain guide on my RIP9, but I'm also not running a narrow/wide ring. When I went to 1x10, the narrow/wides weren't as prevalent as they are now, and when I replaced stuff this spring, the regular rings were on closeout so I stuck with the guide.