I have to say that I don't use geofencing because it drains the battery far too quickly. I do however leave my wifi on the whole time, and do not get significant battery drain from it. Doubltess I would get better battery life if I left wifi off too, but leaving on it on has generally not caused me too much concern.
On my Lumia 1020, using geofencing is a non-starter for this reason. From my own experience, on my old Nokia N8 and Lumia 1020, any use of GPS (which geofencing by its nature will use) is the single biggest source of battery drain on the phone. In my case, I found that using geofencing to determine whether to enable wifi will drain my battery far faster than simply leaving wifi on but turning geofencing off. Obviously results may differ with your own phone, and your own usage.
Also, when I first tried Cortana on my Lumia 1020, I found that my phone had use up as much battery by lunchtime as it had previously used by about 5pm. When I turned off location services, the problem went away but then I could no longer access Cortana. So my middle ground, which works for me, is to enable Location services, but turn off geofencing. Cortana now works for everything other than those things that require geofences (and to be honest I didn't find them particularly useful anyhow) and I still have a usable phone by the evening commute.