It's useful for them to be aware of idiom that might cause trouble. That's not telling people to avoid it. It is just giving them extra information.
The real reason for avoiding "off the reservation" is that it is an Americanism that doesn't have much use in other English speaking nations.
It's useful for them to be aware of idiom that might cause trouble. That's not telling people to avoid it. It is just giving them extra information.
The real reason for avoiding "off the reservation" is that it is an Americanism that doesn't have much use in other English speaking nations.