Hi Ravi,
There are many aspects of SAP SD /MM (R/3) which have been combined in Simple logistics.
I suggest you please read some good available blogs in S/4 HANA forum.
Also , refer to the simplification list of On premise 1511 edition which covers all the information.
SAP S/4 HANA Simple logistics expected to combi... | SCN
One useful blog is pasted above.
- Shubham