Basically, showing the number of results in the SERP for each keyword.
The goal is finding low hanging fruit keywords by analyzing the relation Results/Search Volume (and Position).
When you analyze your site or a competitor's you can find a keyword with 3000 searches/month with 2500 search results in a very low position, this keyword could have a great potential to be easily ranked.
Example (via SEMrush, see screenshot):
keyword: paul edward hospenthal
Pos: 60
Search Volume: 5,400
Results: 7000
This feature should be applied every time a keyword is analyzed (Site Explorer, Keyword Explorer, Rank Tracker, etc).
This feature is pretty useful and it's something I use in SEMrush.