Features of Yii framework

Yii is easy 
To run a Yii-powered web application, all you need is the core framework files and
a web server supporting PHP 5.1.0 or higher. To develop with Yii, you only need to
know PHP and object-oriented programming(OOP). You are not required to learn
any new configuration or templating language. Building a Yii application mainly
involves writing and maintaining your own custom PHP classes, some of which
will extend from the core Yii Framework component classes.
Yii incorporates many of the great ideas and work from other well-known web
programming frameworks and applications. So, if you are coming to Yii after
using other web development frameworks, it is likely you will find it familiar
and easy to navigate.
Yii also embraces a convention over configuration philosophy, which contributes to its
ease of use. This means that Yii has sensible defaults for almost all aspects of wiring
your application. If you follow the prescribed conventions, you will write less code
and spend less time developing your application. If desired, Yii allows you to
customize and easily override all of these conventions. We will be covering some
of these defaults and conventions later in this chapter and throughout the book.

Yii is efficient
Yii is a high-performance component-based framework for developing web
applications on any scale. It encourages maximum code reuse in web programming,
and can significantly accelerate the development process. As mentioned previously,
if you stick with Yii's built-in conventions, you can get your application up and
running with little to no manual configuration.
Yii is also designed to help you with DRY development. DRY (Don't Repeat
Yourself) is a key concept of agile application development. All Yii applications
are built using the Model-View-Controller (MVC) architecture. Yii enforces
this development pattern by providing a place to keep each piece of your MVC
code. This minimizes duplication and helps promote code reuse and ease of
maintainability. The less code you need to write, the less time it takes to get your
application to market. Similarly, the easier it is to maintain your application, the
longer it will stay on the market.

Yii is extensible 
Yii has been carefully designed to allow nearly every piece of its code to be extended
and customized to meet almost any need or requirement. In fact, it is difficult not to
take advantage of Yii's ease of extensibility as a primary activity when developing a
Yii-driven application, which is extending the core framework classes. If you want
to turn your extended code into useful tools for other developers to use, Yii provides
easy-to-follow steps and guidelines to help you create such third-party extensions.
This allows you to contribute to Yii's ever-growing list of features and actively
participate in extending Yii itself.