What’s the difference between low-power mode and normal mode?

Low-power mode samples some bias circuitry on a clock to conserve quiescent current. Normal mode has these bias circuits always-on, thus increasing quiescent current. The primary trade-off of low-power mode is that the PMIC is susceptible to overloading issues when it tries to soft-start. There is a secondary trade-off that causes glitches on the SIMO outputs at the bias sampling frequency when they are loaded. For these reasons, Maxim recommends leaving the device in normal mode (which is the default for the bias) until the PMIC is powered on, and only switching to low-power mode when the system is in a state of light activity.