One caveat to the built-in GPS that directly embeds location data into EXIF (or an attached external unit that permits direct embedding) is the fact that, if the data are incorrect (for whatever reason), you will have incorrect data embedded in your image. While it may not happen frequently, the caveat is included in Canon's manuals for GPS enabled cameras (like the 6DWG) and their external GPS logger. If you at least log a redundant GPS track (with your phone, or a GPS) you have back up. If you roll without backup, it would seem that embedded GPS data is a convenience but not a necessity. Interestingly enough, the 6D is offered in two variations, one with GPS and WIFI and one without. It appears that this is for reasons related to the legality of devices containing GPS in certain export markets. I have no idea if this is a burden to Canon's manufacturing and distribution practice, but it seems to indicate that it is possible to have it both ways. Another interesting aspect of this is that unscrupulous retailers apparently have advertised 6D's with GPS and WIFI (the 6DWG) at too-good-to-be-true prices and then sent the unwary buyer the 6DN (which does not have GPS and WIFI). Definitely a potential downside to having multiple flavors of the same model. Caveat emptor.
Look at that, I started and ended a paragraph with the word caveat.
kirk