The main reason for updating these drivers is so that you can use USPL or MTTY. USPL is an alternative to HSPL and is used for flashing roms. MTTY is used for retrieving information from the HTC bootloader as well as setting certain things. One of the more popular uses for MTTY is to clear the rom update error code in the bootloader after a failed flash.
The drivers that come with Windows for the HTC Bootloader are incompatible with USPL and MTTY. Once you update the driver with this guide you will be able to use USPL and MTTY.
Now that you have the drivers downloaded and extracted you need to know which version of Windows you have.
If you have Windows XP go to post 2
If you have Windows Vista or Windows 7 go to post 3
If you have previously updated drivers and successfully flashed a rom before you do not need to update drivers again. If 'usb' is not displayed at bottom of bootloader when connected to pc, simply reboot, press F8-key & select option to ignore the signature. Phone should now state 'usb' in bootloader to enable you to flash rom