Is it safe to use Game Booster in Win 7 x64?

When I was playing 'Watch Dogs', I observed vicious stuttering after 30-60 minutes of game play. Rather than considering it as a gaming defect, I optimized the operating system by stopping few services and Start ups.

The Youtube helped me through out the process as I could find useful videos to optimize windows 7 for increasing the gaming performance. Now, it helped me a lot and I don't find any stuttering or lagging issues while playing high end games.

Recently, I found something known to be GAME BOOSTER which is said to tweak the OS automatically for providing a better gaming environment to the user. I know there are lot of gaming booster software around the world but are they safe to use?

If safe, can anyone suggest me a familiar and most popular game booster software? Thanks in beforehand.