For some publishers, who mostly have traffic from UK,US,Canada,Australia, it may have a positive affect on their AdSense revenues, but for publishers from Asian countries like India, Pakistan, Personalized-Ads had more of a negative impact on the revenue streams of AdSense publishers, let me explain you how.
Now, since Google already get an idea of what a user is looking for on the web, they start showing ads relevant to what a user is already looking for, rather than showing ads more relevant to your website content. This may not affect much if you have traffic from high-paying countries like USA, UK etc because there is always a high competition among advertisers in those countries and publishers get a good rate per click.
But this badly affect publishers of low-paying countries like India, Pakistan, Philippines etc. Because there is already, generally, a low competition among advertisers which means click rates from these countries are going to be low. But the most important point here is, users in low-paying countries generally share their wifi and internet-enabled devices with others too, and that affects publishers badly, let me explain how.
How Personalized Ads get you Low Earning in AdSense?Suppose there are 4 members in a family who use device to use internet, lets say a laptop. A kid keep on searching cartoons on Google. A teen searches makeup tips most of the times, another member mostly search for funny videos, but the 4th member likes reading your blog. Now, whenever he opens your blog, he'd see ads related to cartoons, makeup tips and funny things (rather than seeing ads related to blog content), because this is what Google thinks is most relevant thing as this is what it calculated from sessions and cookies.
Since Google is showing ads related to search behaviors of other members, this is going to affect click through rate and RPM of AdSense publishers because users are not seeing relevant ads hence they will ignore ads.
Should you disable Personalized Ads?I'd say YES, opt-out personalized-ads if most of your traffic is from less-paying countries and analyze results. Disable personalized-ads and wait for 48 hours until Google completely purges older personalized-ads from your blog. After 48 hour, give your new settings 2, 3 days. Once your blog start serving non-personalized ads, compare your latest AdSense data with previous data.
Concluding this post, I must say that AdSense has become more of an experimental lab, and you must keep on doing different experiments in order to make more money from your blog. Give it a try what is being said in this post and see the results yourself, till than, wait for me to come up with another useful method to increase your AdSense earning.