Yes, but how significant is the consequential reduction in ‘battery life’ compared to how often you charge your Forerunner device?
I don't have a FR735XT, but I have a FR235 which I've been using for more than 11 months, and even with Bluetooth enabled (and connected to my mobile handset) all day a full charge will still last me rather longer than a week if I don't otherwise use it to record my runs (with GPS and Wrist Heart Rate both enabled). If I run everyday, then I ‘lose’ about 10% on the battery gauge per hour of recording, so I have to charge my watch every four or so days anyway, and being able to squeeze an extra half a day out of a full charge would be neither here nor there. Furthermore, I do like having my received messages come to me on my watch immediately – and that requires keeping it connected to my handset via Bluetooth.
Anyway, my point is that you answered TIMGROSE's question by saying (you enable Bluetooth) to upload/download data via smartphone, and I'm reframing it as no you aren't, you're disabling Bluetooth to try to conserve battery (your choice, but not a must) as opposed to accessing a particular technical feature that the watch can provide. I don't think the watch is designed to require Bluetooth being switched off when not in use, and it's fine for Garmin to (implicitly) have a philosophy of letting the users charge as often as they have to – as long as battery life reasonably conforms to specifications as marketed – without trying to minimise the number of recharge cycles and maximise the useful lifetime of the non-user-replaceable battery in the watch itself.
Don't forget BLE stands for Bluetooth Low Energy - i.e. the power drain is not huge and so is designed to left on in the background.
My experience is similar to ASmugDill in that I go for a run or ride and so use GPS then the battery goes down way more than say a rest day when I just have Bluetooth on in the background.
In other words, I don't see a point in keep turning Bluetooth on or off.
