Using UPDATE, DELETE or INSERT to move data can take quite a lot of time and use resources (IO) on both data and log files/disks. It is possible to avoid filling the transaction log with potentially lots of records while working on a big table: Using partition switching, only the metadata is changed.
There is no data movement involved and this is therefore performed really quickly (almost instantaneous).
###Sample table
The question does not show the original table DDL. The following DDL will be used as an example in this answer:
CREATE TABLE dbo.idT(
id int not null