AddMemberListRequest vs AddListMembersListRequest, two classes for same purpose ?

I m wondering why CRM provide AddMemberListRequest  and AddListMembersListRequest, two classes for the same purpose. From documentation I can see both classes have different class members but is that ? I mean is there a reason why we have two classes ? Is one better then other and in projects which one is preferred to use ?

https://msdn.microsoft.com/en-au/library/microsoft.crm.sdk.messages.addlistmemberslistrequest.aspx

https://msdn.microsoft.com/en-us/library/microsoft.crm.sdk.messages.addmemberlistrequest.aspx

Thanks for guiding me