Just value adds, you can listen just fine without them. You might lose (in the case of the headphones that lead to the article) some fitness tracking features, ANC or EQ fine-tuning, or other additional functionality but they'll work just fine for audio.
Bose has a computer-based firmware updater over USB, I used it with their relatively new noise cancelling 700 headphones since I don't use the Bose Music app. Website launches a Windows desktop application for the update. Worked great in a Windows virtual machine with USB passthrough.
For older QC35 headphones there's a 'based-connect' repo on github that lets you configure the headphones; unfortunately the newer models such as the NC700 have encrypted firmware update files so I couldn't easily reverse engineer the protocol to get all the BT commands to configure all the options you can change in the app. Actually the app didn't even work on my Android phone without GApps, so I couldn't sniff the connection either...
