Why canonical issue is so important?

[siva s]

Hi,
Tell me, Why canonical issue is so important?

[RH-Calvin]

An option for dealing with duplicate content is to utilize the rel=canonical tag. The rel=canonical tag passes the same amount of link juice (ranking power) as a 301 redirect, and often takes much less development time to implement. The tag is part of the HTML head of a web page.

[mukeshkr]

Canonical tag will help your website to penalize with duplicate content with search engine. Some pages having same content like other versions of the URL loading the same page with additional parameters such as /index.php or even /home.php.