What does “reduced advertising” mean?
How about reduced advertising ? I mean, when I reach 200 rep, what things will happen? I will get 200 rep soon.
How do I know it's working?
The answer here http://meta.stackoverflow.com/privileges/reduced-ads
"After you achieve the privilege, the style ads will be automatically suppressed from question pages when you are logged in."
SO gives you commercial Ads to the right hand side of page. Once you reach that limit, those will come with lesser frequency. From my experience, I observe that I am getting more links on other SE site questions and less frequently getting commercial Ads.
Overall, the Ads on SO are no pain at all, unlike most other other sites, where every para is perimeter-ized by Ads.