Stolen is the least of your worries...it's much more common for a computer to freeze halfway through writing an assessment task, and for half of it to be lost.
Or for a virus to wipe part or all of your drive or just stop a useful program like word from working.
Or for some part of hardware to give out, making the computer useless. For example, since the beginning of this year, I've had my motherboard, heat synch, charger and battery die. All of which have caused the computer to stop working/spontaneously reboot, making files inaccessable/causing unsaved data to be lost (yes, my laptop sucks ass, but I get a new one next year).
If you want to use a laptop, you have to be a paranoid back-up maker.