Select this if you want Suspend-to-RAM to save the most power
possible (without powering off the CPU) by disabling the PLLs
and main oscillator so that only the 32 KiHz clock is available.

When only that slow-clock is available, some peripherals lose
functionality. Many can't issue wakeup events unless faster
clocks are available. Some lose their operating state and
need to be completely re-initialized.