Why should you not use Entity Framework or an ORM?

Entity Framework is it's not a panacea nor is appropriate for every kind of application even an application that heavily uses data just because it's relatively shiny and new and heap doesn't mean you should carefully think about how and whether to fit into the architecture of an application.

·         Isn’t appropriate for every kind of application. EF heavily uses  reflection  and hurts performance. For this  point there are many lightweight  ORM's  that  can be used  as an alternative  such as Dapper.

·       EF doesn't do bulk inserts. It's usually better to use the databases support for this kind of large fast data imports instead or even use some of the native .net features for the task.