Scyoung0746Liners help extend the life of your bag and limit the amount of washing required. When it comes to goose/duck down bags the oil on your skin can greatly decrease their effectiveness over time. Do they need liners... no... do liners have benefits... indisputably yes. Should you buy one... depends.
ElectronicVicesOK. Let's be honest. Each layer you add will provide less abrasion of the fabric inside your sleeping bag. That's true. So how many layers do you want to stuff to save your $300 bag? If it is that expensive, it is probably UL. And here comes the question - would you carry 150g of this liner with you the whole AT? I don't sleep naked anyway. At least I wear my thermal long underwear (icebreaker merino wool). So why carry another layer? BTW, in most cases I sleep even with more clothes on.
And the killer bottom line - you want to save your $300 sleeping bag? Take silk pajama. I'm serious. It will weigh less (or at least not more) and will be way more comfortable.
Just my $.02
tau_neutrinoWhen I am too tired/lazy to change clothes,
Too warm for socks (and with or without footwash),
Sleep naked,
My liner is my cocoon, comfort, and peace of mind. My biggest thing is feet - camp socks are great but I prefer sleeping barefoot. My liner allowed me to keep my synthetic quilt clean the entire AT in a way PJs wouldn't have...then again PJs with footies I could see a strong counterargument for. ;)
tau_neutrinoI wasn't talking about abrasion, unless you went with something like a 7D fabric it should be plenty durable. My point again is protecting and preserving your insulation. I use an Argon (Nylon) quilt liner because I would rather not have to wash my down gear regularly and it works wonderfully in warmer weather. The more you compress and wash an insulation medium (synthetic or down) the sooner it breaks down. When synthetic fibers or GD/DD breaks down you lose loft, when you lose loft you lose insulation/warmth. I would also venture that my quilt liner weighs less than any pair of silk pajamas you could locate.