You should also consider the use-case of no automatic background syncs.
When I go to look at the dashboard in Garmin Connect online, or the My Day screen in a Garmin Connect Mobile app, logically it ought not be a prerequisite to manually initiate a sync (from whichever end), just to view current statistics on the dedicated dashboard mechanism. Especially when Bluetooth is always enabled on my FR235 in its capacity as a 24×7 activity tracking device and receiver of smartphone notifications, I expect it to remain connected to a paired mobile device (and automatically reconnect as necessary) as much as possible and make itself useful.
I personally keep the BT always off and use no notification or any other "smart" features (weather, calendar etc) because my Forerunner is a training tool, not an Apple Watch, and I want to maximize battery life.
That's your priority and your prerogative, and that's a perfectly sound device management tactic you're employing. As a user, I want notifications to be displayed on my FR235 as they arrive. No, I don't want an Apple Watch, and I don't want a ‘smart watch’ to run apps like you would on a smartphone with which the user can interact with online data services, make information requests and expect them to be fulfilled, initiate sending of outgoing communications, etc. One-way communication of information (not related to fitness or sporting activity tracking) from my mobile device to my FR235, with the latter in the capacity of a display device for such, is sufficient.
When I don't want background syncing of fitness and sporting activity information, I dismiss and close the Garmin Connect Mobile app on the mobile device, but leave Bluetooth enabled on both ends so that notifications continue to work. Like you, if and when I want to conserve battery on the FR235 because I forgot to charge it, I manually disable the functions on it (e.g. Bluetooth, wrist turn triggered backlight) that I can live without in the meantime.
