Disk manufacturers specify the number of power failures the disk is good for, and the number is usually counted and reported by a smart attribute. It is much better to use shutdown, which will issue a Standby or Sleep command to the disk. That flushes the disk cache and unloads the heads gracefully.
smartctl -A /dev/sda
192 Power-Off_Retract_Count 0x0032 100 100 000 Old_age Always - 8