Keeping your chain in place is pretty vital for riding a bike. For years riders had to put up with dropped chains thanks to poor chain guide designs or the complete lack of a chain guide! Thankfully, these days there are a huge number of products to not only help keep your chain in place but also to help protect your frame, chainring and chain from impacts.
While chain guides are usually associated with mountain bikes, road bikes can benefit too with lightweight chain catchers helping prevent the chain from dropping off your chainrings and damaging your expensive carbon frame.
When it comes to proper chain guides and bash guards, though, the mountain bike world is where these come into their own, particularly when riding down incredibly rough and rocky terrain. A misplaced rock and dodgy (or unfortunate) line choice can lead to a bent chainring or worse, so protecting you chainring with a chain guard or bash guard, however you'd like to name it, is a smart move if you frequently ride rocky trails.