What is BD64, Dependent on class membership ?

Hello,

When I expand my distribution model in BD64 I can see the Dependent on class membership check box for below 3 message types

CHRMAS

KNOMAS
ECMMAS

I was able to see some mapping of some classes to logical system with Push indicator in SALE.

For IDoc filteration I checked filters in BD59 however I do not understand what is Dependent on class membership in BD64 any help would be appreciated, I went through quite some SCN threads and SAP help but could not find out usage of Dependent on class membership.

Best Regards,

Ameya B.