Use of AsNoTracking().

Its very depth concept, the EF context keeps track of changes like when you add something to the dbset then state becomes added similarly if you delete something from DbSet then the state becomes deleted now when you call SaveChanges() based on the state only EF fires necessary T-SQL and your changes commits to the database.

If you use NoTracking it means you are telling EF to don't track anything whatever change i will do on my DbSet so when you will call SaveChanges() nothing will be commited to database.

 

If you don't need to update the entities retrieved from the database, then a no-tracking query should be used. After below code anychange to the Employees will not reflect in database.