The webmaster tools labs are a testing area for Google. The labs may change or disappear. Its google playground to see if a new lab would be useful to webmasters and if they should develop it more and move it into one of the other sections.
Instant Previews
This is for checking a live page against the same page that Google has. It’s to check that Google isnt having difficulty crawling your page.
Site Performance
The site performance is all about speed. Speed in becoming an increasing important factor in seo as well giving customers a better service when they go to your site.
Video Sitemaps
If you upload a video sitemap this were you can check the errors and any potential issues.
You might also like to read :
Dashboard - Overview of the dashboard in Google Webmaster Tools
Site Configuration - read what the site configuration section covers.
Your Site on the Web - read about the Your Site on the Web section.
+1 Metrics - What is the Google +1 and how Google reports back to you
Diagnostics - Read what’s in the diagnostic section.
Labs - Google playground.
