Some stress tests use AVX and give a unnecessary boost to vcore. Other than that I'm not sure but auto vcore will give it too much.
Even if you don't overclock you should at least use manual vcore, or a adaptive offset.
For example my 4790k @ 4.6ghz with auto vcore gets 1.51v. Too much!!. It only needs 1.23v for 4.6ghz.
1.23v is only a little bit more than stock under load.