what is the use of latest penguin update?

Google penguin 4.0 now real-time, Penguin data is refreshed in real time, so any changes will be made as soon as the affected page has been recrawled and reindexed.

Penguin 4.0 will only directly affect the specific violation links and be adjusted search rank based on spam signals.

Penguin 4.0 is the real time update for Google. With this change, Penguin's data is refreshed in real time, so changes will be visible much faster, typically taking effect shortly after we recrawl and reindex a page. It also means we're not going to comment on future refreshes.

Penguin update targets websites that contains bad links from low quality sites and these unwanted links are ignored when it comes to ranking metrics.

Penguin filter would run and catch sites deemed spammy. Those sites would remain penalized even if they improved and changed until the next time the filter ran, which could take months.
Penguin 4.0, Google would not give a specific number of the percentage of queries it impacted, mostly because the update is constantly happening and the percentage will constantly be changing.

Google's next generation Penguin update is calling Penguin 2.0. It contains Penguin 2.0 technology under the hood, which Google says is a new generation of tech that should better stop spam. Matt Cutts, the head of Google's Web spam team, announced the new Penguin 2.0 update during This Week in Google. Google share information in the entire world to make your content unique to improve your website ranking.

It is a real time update for Google. It ignored unwanted links when it comes to ranking metrics.

Google launched the Penguin Update in April 2012 to better catch sites deemed to be spamming its search results, in particular those doing so by buying links or obtaining them through link networks designed primarily to boost Google rankings.