Purpose of / why only 1 char for MANDATTRLOCPRODSUBR (Mandatory Attribute Loc Prod Ref)?

In Location Product Substitution R | SAP Help Portal one can find an explanation of the attribute MANDATTRLOCPRODSUBR (Mandatory Attribute Loc Prod Ref).

However, it doesn't seem to explain the actual purpose of this attribute.

If I examine the UNIPA default unified planning area, the attribute is of Data Type NVARCHAR and only has Length: 1

Is it safe to assume that this is a flag? Is the actual use or purpose of this attribute documented somewhere please?