OS X tends to try and help out and reopen everything to just the way it was before it crashed. I mean this in two ways:
If an app running within OS X crashes, OS X will remember the last working state of the app and resume at that point next time you launch the app.
Example: Safari crashes because I've shamelessly opened way too many tabs and windows again. The next time I launch Safari I tax the system severely and fight to be able close windows or even force quit again.
If OS X itself crashes, the computer automatically restarts and loads OS X again, at which point every application, web page, and document that was open at time are simultaneously reloaded.
How can I prevent or alter the way such situations are handled?