Placement targeting didn't give Desired result , people strongly felt the absense of Keywords and hence relevancy which had made it less rewarding earlier. Perhaps, Google listened and added keyword feature into it! It is no more a placement targeted campaign, but content + placement in a single campaign. Now, you may add placements directly into your content network campaign which will skew the impression distribution towards your chosen domains. You may also adjust bid against individual placements.
Now Onwards, there will be difference between campaigns with Keywords and one without it. If traffic is extremely relevant for your website, it is better to make a Placement campaign without any keyword. Make sure the stats against a particular domain in Placement Performance Report are Good. An extremely good traffic means you need to set a CPM campaign to make the most of it. If it seems risky then try CPC campaign.
The impact of recent changes will not only be felt by advertisers but publishers too will find higher paying ads on better websites which will boost the eCPM of their pages. Many different Ad Auction Platforms were offering codes which alternates ad delivery of different Programs based on eCPM they produce on the Page. This step should boost the eCPM of Adsense Ads, so that Loss of impression for Google may be avoided.