ADP5091 REG_D0 and REG_D1 settings

1) I'm not entirely sure how to understand REG_D0 and REG_D1 settings.
Table 6 "Regulated Output Working Mode Configuration" describes:

Working Mode REG_D0 REG_D1
Boost Disable Low Not applicable
Boost Enable High Not applicable
LDO Disable   Not applicable  Low
LDO Enable Not applicable High

If I want to use LDO I understand REG_D1-> High.
But what does "Not appclicable" mean for REG_D0 ? Should it be Float, or I should use setting to disable boost -> REG_D0=Low?

2) What happens if I turn on Boost and LDO at the same time. Will there be any permanent damage?

3) Can the POWER_GOOD signal be used to enable LDO?