There has been some question in this thread about whether Waze is equivalent to other apps which make heavy/continuous use of the GPS, or if it is actually drawing more power than those apps. I was on a road trip this week so decided to run a test. With the same conditions (e.g. phone position in car, type of charger, destination, etc.), on my Lumia 1020 running the "Black" update, I used Waze for 30 mins, and then Here Drive for 30 mins, noting the battery life at the start and end of each cycle. I did this cycle two times to try and reduce variability.
I found that in 30 mins, Waze was able to drain the battery of my 1020 by 4-5% even while on a charger. When I switched over to Here Drive, the battery was able to charge back up by approximately the same amount within 30 minutes. Switching back to Waze showed the same drain consistently, while with Here Drive I was consistently able to charge (albeit very slowly). The other thing I noticed was that the phone definitely got much warmer using Waze than with Here Drive - with Waze, after 30 mins, the phone was almost too hot to touch, while with Here Drive, it got warm but not hot.
Note that this was driving on a highway, so the conditions were not identical from cycle to cycle, but I kept an eye on things like phone signal strength, and things averaged out pretty well, so I don't think there were any external conditions that were affecting the testing in any significant way. One other experiment I tried after the testing above was putting my phone in airplane mode, to see if some of the extra drain was coming from usage of the cellular radio. Leaving the phone in airplane mode did not noticeably reduce the battery drain nor the temperature of the phone, so it seems like the usage of the GPS itself is the primary cause.
Bottom line: I don't know what Waze is doing differently than Here Drive - perhaps offline map data helps? - but it seems like there could be some opportunities to improve the power usage of the Windows Phone version.