Last weekend I tried to get some data on the power consumption using Hungermeter, but it would seem to me that there's not as much a difference as I'd expect if both wifi and mobile data are on or if only one of them is enabled. However, it is hard to get any good figures since the power consumption of the phone varies quite a bit, a 60 sec average is not at all stable even though the device sits "idle" on the table. Killing all non-essential background processes might stabilise it a bit but I didn't want to crash my phone by starting guessing what is essential and what is not

I'm only using wifi as a "when" condition at home, having it turned on when I'm roughly in the neighbourhood (defined by cell IDs). When my AP is found, mobile data is turned off.