What is the use of flags in Parcelable?

I have been writing Parcelables to Parcel without any focus on flags field, which is a parameter in the method signature and it has worked fine but I have run into an implementation where I can no longer ignore them:

public static <K extends Parcelable, V extends Parcelable> void write(Parcel dest,
                                                    Map<K, V> map, int flags) {
        if (map == null) {
            dest.writeInt(-1);
        } else {
            Set<Map.Entry<K, V>> entrySet = map.entrySet();
            dest.writeInt(entrySet.size());
            for (Map.Entry<K, V> entry : entrySet) {
                dest.writeParcelable(entry.getKey(), flags);
                dest.writeParcelable(entry.getValue(), flags);
            }
        }
    }

This is a Map to/from Parcelable utility I have written and I am wondering if the flags should be passed as it is to both Key as well as the Value while writing them or should pass 0 for Key and flags for Value.

I read the definition of what a flag is in the docs:

PARCELABLE_WRITE_RETURN_VALUE

added in API level 1

int PARCELABLE_WRITE_RETURN_VALUE

Flag for use with writeToParcel(Parcel, int): the object being written is a return value, that is the result of a function such as "Parcelable someFunction()", "void someFunction(out Parcelable)", or "void someFunction(inout Parcelable)". Some implementations may want to release resources at this point.

Constant Value: 1 (0x00000001)

But am unable to comprehend it. Could anyone explain in simple terms what a Parcelable flag is and how it should be used?