Hi Shubham,
As far as I understand: firstly SAP APO, CRM, BI which were earlier treated as separate or extensions will all be under one umbrella and in one server-S4 HANA and I believe part of the licence of S4 HANA.
Secondly, SAP customers might loose out on some of the smart features that are offered as S4 HANA integrated with APO- for example:
ATP functionality will not be part of the SD anymore it'll be part of GATP & Flow manufacturing works in unison with APO.
It really depends on what is your client's industry and if they're already on SAP without APO--maybe they need to check the simplification list on functionalities that will be discontinued.
However, if APO is part of S4 HANA you may want to convince your client to utilize it.
Hope this helps.
Regards
Raghu.