Recently the Pdds got changed, so that Feedback and Leech can drain their energy as well as the EMP.
There are just a few reasons to get the lategame Ravens, protection against gh/Nova or Fungal/Storm. With the pdds able to get EMPed was alright, because as soon as you emped them you had to commit! It was an investment of 60 energy + 60 (emp the hero) + 125 (lash) + 25 (cloak), so 270 energy out of her 300. If there wasn't an opportunity to kill something after the emp on the pdds Nova has to go back and wait to regenerate the missing energy before she could go in again.
Now the Infestor and HT have the opportunity to feedback/Leech pdds, its way cheaper to do so and after that, unlike Nova, they are very likely to get some Value out of storm/Fungal. The infestor can even get an advantage (up to 200-25 = 175 energy) out of the pdds, that are supposed to counter him.
I prefer how it was before, and if emp should work like feedback and leech (every ability can drain the pdd energy or none, how raiden wants it, I disagree with that), even in that case I pref none of these abilities draining the pdd energy. The Nova emp on the pdd it was a rare case. In all the games I played there were just a few oppertunities to use it and be worth something, while I've already seen more leeches and feedbacks on the pdds than emps getting some value by that.