Question: In Global Config in joomla have 2 caching is conservative and progressive, what is difference both ?

Answer: 
For **Unique cache per visitor** 

* **Conservative cache** shows all visitors to your site the same exact cached content.
* **Progressive caching** however caches the content for each user uniquely.

From the [link](http://www.inmotionhosting.com/support/edu/joomla-25/caching/global-module-caching) Provided by @Tornado's comment
Progressive caching works just like conservative caching with a difference that buffers are updated progressively.

If you look at the render function in JApplicationCMS (where progressive caching is set), you will find that its not applicable to logged in users.
<https://github.com/joomla/joomla-cms/blob/staging/libraries/cms/application/cms.php>

```
if ($this->isSite() && $this->get('caching') && $this->get('caching', 2) == 2 && !JFactory::getUser()->get('id'))
    {
        $caching = true;
    }

```

Further if you dump the cache id's for the same page across browsers or ips you will get the same cache id's.

The typical work of progressive caching happens in JCache's getWorkarounds and setWorkarounds. However beware, the cbuffers can get unwieldy large at times causing issues.