[bluruld]

You only need the sim unlocker if you plan to use a USA sim service(tmobile/at&t) in conjunction with your sprint service. Or I suppose you could completely move to one of those networks if you chose. Additionally you might want to sim unlock to flash a different radio but doubt many non advanced users will be doing this.

Most people won't want of need the sim unlocker judt the HSPL unlocker to flash any rom of their choosing.