Same with MBP touchpads which many people don't even realise since the feedback works even when the laptop is sleeping. It's a really weird experience when you actually turn it off and... nothing - you can't actually "press" it.
When I had the first generation MacBook 12", people wouldn't even believe that it was not a mechanical click when you told them. I often had to turn the machine off to convince them that it is fake. Which I would happily do to see the look on their faces ;).
I remember pressing the home button on a powered off iPhone 7 a few times. It feels like attempting to take the last step in a flight of stairs when you miscounted by one.
Took me a while to realize this also applies to the magic trackpad and integrated trackpad on macbooks, but it is nice to be able to customize it. The trackpads even have two clicks the second being a "deep" click which requires even more pressure than a regular click.
It's pretty easy to notice with the magic trackpad—it loses its ability to be "clicked" when it loses power/when you turn it off.
(The trackpad on the laptop does as well, but I feel like you're just less likely to try clicking the trackpad on a macbook/MBP if the computer's not on. Whereas with the external one, you'll notice it when you go to pick it up/move it around and it doesn't accidentally click in your hand.)
Also a nice feature, which unfortunately not a lot of applications use, is the haptic feedback. E.g. when you drag an object in OmniGraffle, you will feel very subtle feedback in the trackpad when two objects align.
Almost 20 years ago I had a cool Logitech mouse that did this. The mouse had a haptic (Synaptics, I think?) engine in it, and when you moved the cursor over buttons, menus, or other UI elements, it would give a slight “tick” as you crossed each boundary. It was very cool. There was a lot of customization available for it as well.
I had to ditch that mouse when I switched to Linux. I think it didn’t have any standard HID-type driver or something.
Yeah when I got my 2015 MBP that track pad was mind blowing. I remember turning it on and off and comparing the feeling of trying to click it. It's an incredible innovation. Small, but amazing from an engineering/UX perspective.
How: haptic feedback using a weighted linear actuator.
Why: I suspect because it debuted with the iPhone 7, the first officially water resistant iPhone, that it was a waterproofing move to get rid of possible ingress points.
I've always assumed it was partially about reliability and partially about saving space, since water-resistant physical buttons are fairly standard components.
The phone needs to have some form of haptic motor anyway, and switching to a virtual button allows them to eliminate a complex moving part - removing one potential point of failure - while freeing up a few cubic millimeters of internal volume.
Anecdotally, the home buttons always seemed to be one of the more fragile parts of an iPhone, to the degree that many people started to use the on-screen assistive touch dialogs to avoid wear and tear.
On the older iPhones, the home buttons got problems after a couple of years. My old iPhone 4 had this problem. They got unreliable in registering being pushed. I think that’s also the reason it makes sense to not be an actual hardware button. Less moving parts makes it more reliable and it’s more likely to work after many years.
You shouldn't need to turn it off, it feels like a knockoff of a real button, like a fake designer bag. Don't know what was wrong with a regular button that presses.
If you have an iPhone 7 or 8, try turning it off and try to press the button.