Noob question: Pushbotting

I'm reletively new to playing poker online, only been at it about a month. I've been reading this forum a lot and I notice that almost everyone wants to push most hands in three up/heads up play. What type of hands, generally are people pushing on the bubble, three-up and heads up? Its hard for me to believe you are pushing this often and getting a 40% ITM or 20% ROI