I've noticed a small issue with my email client for quite some time now where composing a new email will have several blank lines by default.
It's not too much of an issue to simply delete them but hey, maybe no one had pointed this out before! So I filed a bug report only to get this response... basically it's not a bug, its a feature!
It means you can click a line and type there, no need to press enter a few times first.
Not email, but if I'm taking notes in a text editor I will hold down enter at the start to ensure I can just click and type anywhere.
Now, if that pointless whitespace is being sent, I can imagine it annoying people in long email chains.
Well, this screenshot is the mobile version. Tapping anywhere in a textbox should bring the focus and start typing. All having extra lines does is make it more likely that the starting insertion point is a line or two below the start.
Even on desktop, I'm not aware of any text box behavior where you need to click on the correct line to bring the focus to the box.