Spread Spectrum Clocking is a way to lower electromagnetic interference or EMI. This is important for storage solutions that are required to pass FCC and other agency certifications. All current Serial ATA disk drives implement SSC (some allow you to turn this feature on/off). However, some older SATA drives do not implement SSC. All Sonnet Serial ATA host adapter cards support SSC but will also work with disk drives that do not.
Often, yes. Sometimes, not. Some other manufacturers' drivers may incorrectly assume a Sonnet card is their SATA card which may cause havoc. The symptoms include significantly slower performance, driver not loading, or both drivers loading and causing and kernel panics as they both try to access the same card. Sonnet recommends removing other manufacturer's card(s) and driver(s) if a problem of this type occurs.