Hi.
I have a yeti sb66c and I got sick of pulling the mud out of the carbon fancy chainguide. So I removed it. Only lost the chain once on a visit to Rotorua. However, looks to me like my front chainring is now wearing down on the outside face at a dramatic pace. Does the chain guide / retention device actually help to hold the chain straighter on the chainring when it is on the largest sprocket at the back and so reduce the angle at the chain ring? The wear seems to only be on the outside of the ring.

If it was set up properly the chain would have cleared the guide even at the extremes.
You would've noticed the rubbing of the chain against the guide.

Good point. However, I was looking for a new chain ring and came across a couple of chain guide manufacturers that were claiming their products extend chain life. Why?

Because marketting

They extend the useable life.

Astoria Paranoia wrote:If it was set up properly the chain would have cleared the guide even at the extremes.
You would've noticed the rubbing of the chain against the guide.

this
if you're noticing wear on one side but not the other, you probably need to move your chainring inboard a bit.
double or triple crankset?

shmoodiver wrote:They extend the useable life.

This is it.

Brand new chains even stay on shimano's shit "we don't need narrow-wide" chainrings for a while. Worn out chains will drop far more often. With a chainguide you can run the drivetrain until it eats itself, if you can put up with ghost shifting.

I'd say you need to space the chainring inboard. I've got a Shimano double crankset and found that 5mm of spacers worked best.