Joints/tendons, gut health, anti inflammatory, overall healing/health, hair, skin, nails. Not a muscle builder per-se like a whey/casein/egg/beef etc. but wouldn't say it doesn't help but it's much more beneficial in other aspects listed.
You only need 5-10 grams a day to get benefits so it's worth trying for anyone thinking about it. This isn't a 150 gram a day protein.
Powders are typically cheaper and very easy (typically tasteless). Vital Proteins makes some great collagen supps.