My main long-running gripe with Adsense has been that it isn't possible to set a minimum eCPM rate for Adsense. Instead a publisher had no choice but to take the good paying ads with the bad. However, if you decide to implement Google Ad manager as your adserver, you're now able set a minimum eCPM by assigning a "house" or "remnant" ad with a minimum CPM of whatever floor you want. Once you've set the floor as desired, you set Adsense to compete in the realtime auction with these slots and the ads will only appear if they will earn you more than the value of the remnant or house positions. While the immediate result will probably be a drop in your Adsense income, as long as you're running other, better paying ads (from direct advertisers, another network or whatever), your end resultant income for the total number of impressions, should be higher. While there's other pros and cons to using the server, this alone is a very big pro.
You still aren't able to set a 'floor'. The system just decides to run Adsense or not. There is no guarantee whatsoever you'll be getting better paying ads.