There are the condition to set in password policy
CompositionUpper case letters Allow The minimum number of characters required is "number"
I would like to know , what is the different between
option1. Checkbox "Allow" Upper case letters and set the The minimum number of characters required is "0"
option2 uncheck "Allow" Upper case letters
Option 1 means that your users are allowed to have capital letters but since the minimum is zero, they are not required to have any... just allowed if they want to.
Option 2 they are not allowed to have upper case letters at all. If their password does have uppercase letters it will fail the policy and they will not be able to change to that password.