What use would they be if she gets elected? She will be protected by the press, a complicit Congress and a supreme Court that is packed with her appointees.
Russia benefits from a Trump Presidency. Syria and Iran are historically Russian client states. Libya and Afghanistan were also. Trump has promised to reduce our presence in the middle east. He is also talked about the same in the Orient as well as NATO. All of these actions benefit Russia.
Why did Russian intelligence hack the DNC?
The emails will be released when they will cause the most damage. Probably after the convention when Hillary officially becomes the nominee. If they take her out before, the Dems will have a better chance to replace her.
If Russia obtained secret and top secret documents from her server, that would be an extreme violation of national security and they could demand certain political and diplomatic favors in return for not releasing them to the American public.