Identity value jumps when restarting SQL Server
I found that it is a new feature (don't know what is use of it)

Before SQL Server 2012, identity allocations were always individually logged (as each value was used). This per-row logging activity could limit throughput in scenarios where many identity values are generated in a short space of time. To improve efficiency, SQL Server 2012 (and later) logs only the allocation of a batch of identity values. The allocated range is cached and issued on demand until a new batch of values is needed.
If SQL Server is restarted without the database containing the identity object being checkpointed on shut down, any remaining unused values in the cached range are lost, resulting in a jump in the values on restart.
Unfortunately, common ways of shutting down SQL Server 2012 do not currently automatically checkpoint databases (this contradicts the documentation, so it should be fixed at some point in the future). To avoid this particular cause of jumps in assigned identity values on SQL Server 2012, always shut down SQL Server using the T-SQL command SHUTDOWN (without the NOWAIT option).
The SHUTDOWN command will checkpoint all user databases correctly before shutting down the server. Do not use the Windows Service Control application, SQL Server Configuration Manager, the SQL Server Management Studio UI, or any other method.
You could also manually CHECKPOINT all databases before shutting down the SQL Server using any other method, but this requires you ensure no identity-allocation activity occurs in any database after your checkpoints, and before the shutdown completes. This may not be easy to achieve reliably.
More information and background in Lost Identity by Kalen Delaney.

Trace flag 272 is now documented in DBCC TRACEON - Trace Flags (Transact-SQL):

Disables identity pre-allocation to avoid gaps in the values of an identity column in cases where the server restarts unexpectedly or fails over to a secondary server. Note that identity caching is used to improve INSERT performance on tables with identity columns.
Note: Starting with SQL Server 2017, to accomplish this at the database level, see the IDENTITY_CACHE option in ALTER DATABASE SCOPED CONFIGURATION (Transact-SQL).
Scope: global only