It basically a hardware interrupt like ACPI, and yes it does improve performance (As you will see on the MS page)

Here is some info about HPET >>>
High Precision Event Timer - Wikipedia, the free encyclopedia
Guidelines For Providing Multimedia Timer Support
Q&A: HPET Timer - Intel® Software Network
Tech ARP - HPET Support
http://www.intel.com/hardwaredesign/hpetspec_1.pdf