Flash means that it takes up 25% of my CPU simply by having the virtue of being opened in a tab.
Actually, I did need that 25% for something else. Was waiting for code to finish compiling (well, for Clang's Static Analyzer to finish running). It takes more then a few minutes to run on a sizable project.
Plus, as jrockway pointed out, it absolutely kills battery life, and I'm on a laptop.