Question: I am a junior developer I can't understand how canvas tag is beneficial for us?
I read lot of articles on that but I can't get the root benefit getting from the canvas tag.

Answer: 
Basically, thanks to canvas, we can now draw/render 2D shapes using HTML5 and the canvas API.

As an example of what's possible now with canvas, [see this](http://muro.deviantart.com/)
The cool projects that came to mind for me are:

* Visualize gps data. GPS data is just an XML list of coordinates. You could easily build something in canvas to "connect the dots".
* An mobile app where the user can actual sign a document with her finger - canvas allows you to export out the rendered canvas drawing to PNG where it can be saved on the server.
* In a game where you have avatars, you can allow the user to actual draw on the avatar. Moustaches anyone?

Other stuff:

* In iOS / Android using lots of CSS3
effects like box-shadow can lead to
poor performance, especially when
animating. You can do a lot of these
graphics in a single canvas tag,
here's an example:
<http://everytimezone.com/>. This thing is flawless on an ipad.
* Cool background effects. For example try going to Paul Irish's
site and move your cursor around the
background: <http://paulirish.com/>
* In this HTML5 book sponsored by Google a lot of the effects are using
canvas:
<http://www.20thingsilearned.com/> -
particularly the "page flip"
animations.