This is the description for the trace flag:-
By default, lock partitioning is enabled when a server has 16 or more CPUs. Otherwise, lock partitioning is disabled. Trace flag 1228 enables lock partitioning for 2 or more CPUs. Trace flag 1229 disables lock partitioning. Trace flag 1229 overrides trace flag 1228 if trace flag 1228 is also set.
Lock partitioning is useful on multiple-CPU servers where some tables have very high lock rates. You can turn on trace flag 1228 and trace flag 1229 only at startup.
and this is the Microsoft description of lock partitioning:-
For large computer systems, locks on frequently referenced objects can become a performance bottleneck as acquiring and releasing locks place contention on internal locking resources. Lock partitioning enhances locking performance by splitting a single lock resource into multiple lock resources. This feature is only available for systems with 16 or more CPUs, and is automatically enabled and cannot be disabled. Only object locks can be partitioned.