Power surges kill lamps
A 400 volt power surge can destroy a projector lamp!
Surge protectors prevent rogue power amplification from damaging your projector.
Lamps have a lifespan of around 2,000 hours - however, from the time you start using the projector the brightness will steadily decrease. You may not notice at first, but eventually the lamp will dim to such a level you'll require a new lamp. Lamps can also blow up - an abrupt and sometimes shocking end which can mean having no projector while you await a replacement lamp.
To ensure a long working life for your projector lamp, follow the listed powering down procedures (never just unplug the projector to turn it off!), install a surge protection power board or surge protector, clean the filters and never move the projector while it's running.