In some countries and most USA states, an "Always On" daytime headlight is the law. Not really strictly enforced here in California but it IS the law ... and has been for about 30 years.

So, every bike you buy will be wired for an "Always On" headlight.

If an owner does mods or changes lighting set up (like I did), then it's easy to
install an ON/OFF switch. I like this as it saves battery on start up. If your headlight comes on with the key (as most stock bikes do) and it's very cold and your battery is low, then that can be the difference between the bike starting or not.

I always have my headlight switched OFF before start up. Then switch it ON once under way. I would like an additional low wattage spot light for night time running, but would never use it in daytime.

Having an ON/OFF headlight switch is also very handy if you ride a low elec. output bike like my DR650. With only a 200 Watt output it's hard to run accessories. On very cold riding days when running heated gear (Gerbing elec. jacket (77 watts) and heated grips (30 watts) I switch my headlight OFF. This frees up 35 watts. (I run a 35 Watt HID light instead of stock
H-4 55 Watt bulb).

This makes a nice difference in how well the elec. jacket works. With a total output of just 200 watts you only have about
90 watts free. Adding 35 Watts by switching off headlight helps quite a bit and you never risk running down your battery.
The DR650 Suzuki will keep running even if you run your battery down flat. But then it will not re-start ... unless you Bump start it. So I try never to over tax the system.

But when riding in 30F temps one really needs that heated gear. Huge difference in survival. The DR650 needs at least 400 watts but no way to get that. After market stators give you 250 Watts but are unreliable Chinese units (not Denso).