Garmin Basecamp wrote some VERY large (105 GB in total over 5 or so files) called usrxxx-xx-xx (where xx represents apparently random numbers) to:
C:\Users\terry\AppData\Local\Temp\BaseCamp
This seemed to occur in relation to 'sending to' a number of waypoints to the Fenix 5x watch. Basecamp stalled in the process and eventually the disk started reporting being full.
I stopped Basecamp and after a few hours searching found the large files where indicated. It looks like whilst 'stalled' Basecamp was actually continuously writing away to the local disk!
Oh, as an added bonus it crashes the watch too. Stays stuck on the 'charging' screen even after you remove it from the usb. Have to give it the 'hold light button for 15 seconds" to turn it off, wait a few seconds, hold 'light' button for a few secs to get it to come back on again.
Fenix 5x s/w version is 10.0
Basecamp version is 4.6.2 so I updated it to 4.7
Running on Windows 10.
Now, instead of hanging, Basecamp 4.7 often (but not always) crashes when I try to 'send to' waypoints the Fenix.
(And yes, I replaced the faulty Mapinstall 4.2.0 with 4.4.0 in the Basecamp, not that I think that had anything to do with it...) See https://openmtbmap.org/tutorials/basecamp-4-7-0/ for why I did that.
This crash doesn't happen when I send waypoints to my other Garmin device (Dakota 20)
It didn't happen when I sent some tracks to the Fenix either. Just waypoints, apparently.
This also didn't happen with the previous versions of Fenix 5x software. I had transferred a lot of waypoints to it not so long ago without problems, when it was version 9.something. I don't remember any such problems then.