The only safe way to turn off your computer is to use one of the standard methods for shutting down. Performing a proper shut down ensures that all files are properly closed and the any information that was being stored in memory has been written to the hard drive. Improper shutdowns include simply hitting the power button on the front or back of your machine, yanking the power cord out of the wall, turning off your surge protector, and crashing. Any of these can leave files in an incomplete state which can lead to disk problems. This is enough of a problem that Mac OS 8.5 will automatically run Disk First Aid when starting your Mac after an Improper shutdown.
Backups are an essential part of any disk maintenance.
Fixing serious problems on your hard drive is like any medical operation. Even though most repairs are simple and routine there is always the risk of a small problem becoming a big one and attempting to deal with a seemingly benign symptom could reveal a serious problem that has as of yet gone unnoticed. Also some problems are serious enough that attempting to deal with them at all will result in data being lost. That said, your only security can be frequent and complete backups. No harm in checking, just fixing.