From Longman Dictionary of Contemporary Englishsave your breathsave your breathspokenCHANGE/MAKE something DIFFERENT# used to tell someone that it is not worth saying anything, because nothing they say will make any difference to the situation I tried to explain, but she told me to save my breath. → save
Examples from the Corpus
save your breath• She might as well have saved her breath.• He might as well have saved his breath - a sea of green benches confronted the Ulster members.• You can save your breath, Fiver. 