Hi Surya,
This is a good question, SAP CRM Sales, Service and Marketing are different modules. SAP has separated certification for each one due to enhanced version and lot of functionalities in SAP CRM. If you look at most of Supply Chain Management companies they would have adopted all three modules, but some companies use only Service or Sales or use both without Marketing. In my current project, we use only SAP Sales, so it purely depends on clients business processes which one they want to implement and use.
SAP Sales Certification and syllabus you can see here: P_CRMSLS_71 - SAP Certified Application Professional - Sales with SAP CRM 7.0 EhP1 | SAP Training and Certifica…
SAP Service Certification and syllabus you can see here: https://training.sap.com/shop/certification/p_crmsrv_71-sap-certified-application-professional---service-with-sap-ehp1-f…
SAP Marketing Certification and syllabus you can see here:https://training.sap.com/shop/certification/p_crmmkt_71-sap-certified-application-professional---marketing-with-sap-crm-…
Regards
GGOPII