They are useful when the chain is tensioned, i.e., by a derailleur and the chainring, but are next to useless on a fixed or singlespeed set up.
I wouldn't call it useless. It can help keep the chain from dragging around when you're fiddling with the back wheel or whatever. Not an essential thing I agree, but not useless.
I wouldn't call it useless. It can help keep the chain from dragging around when you're fiddling with the back wheel or whatever. Not an essential thing I agree, but not useless.