Usually a game to build and design crafts, and do stuff you won't be able to do on most games. Also, for fun. KSP acts as a "time-dump" mechanism if you got nothing to do or bored or whatever. I tend not to go deeper on science stuff, but only on basic and essential ones. My "realism" is only limited to rocket designs. (screw efficiency, dV and oberth effect, I'll just bring more fuel than I should just in case. YOUR SCIENCE HAS NO POWER OVER ME! )