The local time can be ambiguous during a daylight savings time transition. That is, if you use local time in the RTC, and turn your computer on during that ambiguous hour, it will not know which offset should be applied. I believe Windows "solves" that by storing state in the registry, which means that dual-booting with local time in the RTC might in some cases lead to the daylight savings time transition being applied twice (whenever the other operating system has already corrected the RTC clock, but Windows believes the correction hasn't been applied yet). Using UTC (or any local timezone without daylight savings time) avoids that issue, since there's no repeated hour.
