You don't have to use it, but....
I installed it to get the latest USB drivers.
It installs two items: HTC Sync Manager & HTC Driver Installer.
Once its installed & rebooted you can use it. But I unistalled HTC Sync Manager & left HTC Driver Installer then plugged my phone.
You can navigate, drag & drop just like a normal file system.
This uses the MTP file system. (Media Transfer Protocol)
I hope this helps