To "flash the BIOS" means to install an update to the BIOS firmware. You are replacing the older BIOS version with a newer version. Unless you are experiencing bugs ...
Even if your PC seems to be working fine, you should still update the BIOS.
It's inevitable: There comes a time in most PC upgraders' lives when they must partake in a dangerous ritual known as updating their PC's BIOS. It's rarely necessary, but it can benefit performance, ...