don't knock yourself out

Don't expend too much energy or try too hard (doing something), as it isn't worth the trouble. You can clean the house if you want, but don't knock yourself out—the kids will just make a mess of it again anyway. A: "I'm just exhausted this week." B: "Then don't knock yourself out. Mom will be thrilled with any kind of dessert you bring to the party." Don't knock yourself out—there's really no need to go through all the files one by one.