This is after the discussion in dev@ under 'DISCUSSION: A tightening of the CP contract in hbase 2.0.0'
"CPs can read Cells passed them on a CP hook invocation but
they must not retain references beyond the life of the invocation; they
must copy Cells if they intend to retain them beyond the invocation, pass
the Cells off to upper tiers, or return them otherwise to clients."
Also this Jira will cleanup some code which was doing the copy of the Cells while passing to CP hooks assuming it might keep cell refs. Now as we say it explicitly in CP APIs, we dont need this copy.