Absolute value is always the positive value of a number. When enabling comparisons using absolute value, we are telling the database that we DO NOT care and it DOES NOT matter if the field's value is negative or positive. Truth of the matter is, we usually do care and would normally leave this option unchecked.
When Compare Using Absolute Value is Enabled (checked)
-100 is considered to be 100.
When Compare Using Absolute Value is Not Enabled (unchecked)
-100 is considered to be -100 (as it normally would be)