The prevalence of stuff that likes to auto-update without asking you makes this even more dicey. I ran through 50% of my monthly mobile-data quota once when OSX decided to download a big OS update over tethering (my monthly quota is 1GB). It'd be nice if there were an OS-level service letting me mark certain SSIDs as not suitable for unnecessary data use, the way Android knows not to download app updates over the data connection.
Nowadays I mostly avoid tethering unless I really have to use it, since it's always rolling the dice whether it's going to eat hundreds of megabytes of my data quota without asking. Fortunately, there are so many wifi hotspots around that I'm finding tethering at all increasingly unnecessary. And a VPN takes care of the security issues well enough.
Windows 8.1 & 10 let you mark WiFi networks as "metered". Can't do it with USB or Bluetooth tethering, but anyway it does exactly what you are hoping for- the OS will suppress most background network activity. It even tracks "metered network usage" in a separate bucket from regular network usage.
I would expect OSX has a similar setting somewhere, with the increase in metered networks.
Hmm yes you as long as the tethering shows as a network interface (which all of them do) you can manage the metered settings individually, and every device will have it's own virtual network interface even if you sync 2 different phones via bluetooth.
The only time you "can't" do it is if you are using a Wifi Hotspot method in which case you'll have to set the Wireless connection to a metered one so it will keep track of the cap no matter to which HotSpot you connect too.
That said Windows doesn't block applications from accessing metered connections it moderates it self(Windows Update, Windows Mail etc...), has a separate setting for what ever MSFT calls "Metro" apps these days (so "Store" apps can be toggled individually with metered access policies), and for windows services so if Spotify decides to download a playlist you might get a surprise bill in the mail.
> Hmm yes you as long as the tethering shows as a network interface (which all of them do) you can manage the metered settings individually
Everything I've seen on Win 10 metered connections -- including from Microsoft -- indicates that only WiFi (not-metered by default) and cellular (metered by default) connections can be set as metered, and that other network interfaces are always treated as non-metered and cannot be set as metered.
Unless you phone emulates an Ethernet connection it will detect it as mobile broadband and set it up as metered automatically, i never had issues with that...
I don't think OSX currently supports this out of the box. My suspicion is that the next version will, but in an automagical way that only works with iPhones (probably by marking iPhone tethers as a different kind of connection from regular wifi).
> It'd be nice if there were an OS-level service letting me mark certain SSIDs as not suitable for unnecessary data use, the way Android knows not to download app updates over the data connection.
