DO NOT use the low-level utility in BIOS, it can destroy your HDD.
Why do a low-level? To reset the status of the media back to brand new. Gets rid of non-DOS partitions, virii, anomalies that FDISK can't erase. Some even write 0's to the drive, ensuring that there is no data left on it. Good for security as well.
There's no reason NOT to low-level if the drives condition requires it, just make sure you use the correct low-level utility from the correct manufacturer. If it isn't available from that manufacturer, Seagate's
SeaTools seems to work with other manufacturers, and if I remember correctly, Maxtor's
MaxBlast Plus works with other manufacturer's drives as well.