EntityFieldQuery vs Db_select() Why should I use EntityFieldQuery when I can do the same work with Db_select() to fetch the value.

It would be better if someone can provide an example, not only a link.
I think that the main reason prefering EntityFieldQuery over db_select is that you don't have to know about the lower-level structure, in other words: how stuff is stored in the database. This improves loose coupling.