While working with entity, I always had a doubt as to why we use Entity and Entity Field query except Db_select() in Drupal. It is a great and fast way to organize and extract our data in Drupal sites. Here are a few more points to support these concepts :
Entities are very important thing in Drupal. Entity type is connected with lot of tables in data type. i.e entity is a object oriented concept. Entities are used to show thw relation ship with different field tables. An entity is a container for bundles. Entities can contain multiple bundles. Examples of an entity are Node, User, File, Taxonomy term, Taxonomy vocabulary.
A Hello Bar is a simple advertisement bar which provides a notification on the corresponding region in the page and to redirect to other pages. The main advantage of using Hello Bar in Drupal websites is to set and increase traffics for specific pages in your sites.