Slight objection to the characterization that Windows crashes on a regular basis is flawed and depends on the version and use. I've had many machines based on Windwos XP, 7 and 8.1 and have had them run for weeks to months on end without any problem, but anyway...
When you install Windows on a Mac using BootCamp, you are running Windows natively on the machine as the only OS. So you have to do all the things you would normally do with a Windows machine, i.e., run the necessary anti-virus/malware software, keep it up to date and so on. If it DOES crash in this state, it will obviously reboot the computer since there is nothing else..
If you need Windows only occasionally you can go the virtualization route with VirutalBox (free) or VMWare Fusion/Parallels (Paid at $80) to create a VM that will run Windows and your apps. If this thing does die, the VM will just restart and your OS X host will continue to operate.
The virtualization route makes sense in MOST cases except gaming where BootCamp is the preferred route..