HANA Authorization for _SYS_REPO User

Hi All

In HANA system there are some per-delivered users such as SYS, SYSTEM _SYS_REPO,_SYS_STATICS.

I understand SYSTEM user is administration user for all administration related activities in HANA via the studio.but I could not understand the importance of _SYS_REPO and _SYS_STATISTICS, in _SYS_REPO under schema privileges all the schemas created needs to be added as a best practice , and I could not find the usage of _SYS_STATISTICS,can any body explain the usage of the users _SYS_REPO and _SYS_STATISTICS.

Thanks

Santosh