This is the appendix of the Mac UI.
Gather round, kids, and listen to Grandpa tell you a story of the days when Macs had only one floppy disk drive. When you wanted to copy a file from one disk to another, you had to (physically) eject the first disk to insert the second one, but the first disk volume was still logically mounted so you could use it as a source or destination. So the volume's icon remained on the desktop, only dimmed so you knew the disk wasn't physically present.
So you physically eject a disk by selecting it and pressing Command-E (remember, only one mouse button), but how do you get rid of the ghost icon afterwards? Same way you get rid of anything -- you drag it to the trash.
From there it's an obvious shortcut to combining the two operations by dragging a "live" icon to the trash to both eject it and remove its icon in one step. (Well, obvious in 1985, anyway.)
Now that we can right-click the icon to eject the volume and have forgotten the origins of the drag-to-trash gesture, it may seem nonsensical, but those of us who were there at the beginning were grateful for the shortcut. (Also, get off my lawn.)
That was just something that was there forever, basically since 1984. It was part of the Macintosh vernacular. You could also right-click to eject.
Though someone's saying that dragging the ion turns it into the eject symbol, which I hadn't noticed until now but is more reasonable.
Control, which still works incidentally.
2. On a large screen, this action (the trash can transformation) can happen very far away from the place you're looking at, which means that you will miss it. This is a general gripe of mine with Mac OS: It will regularly place popup dialogs on seemingly random screens. I have three active screens, and when I'm looking at the left screen, the right screen is so far outside my FOV that I will literally not notice dialogs popping up there.
If your argument is that the dock is the wrong place for that feedback because it can be hidden, or that the disc/drive icons should always be closer to the dock, then we have a table laid for a good discussion.
Broadly, I object to the inconsistency and high astonishment factor more than any specific choice. For example:
- If a program has dialog boxes open (e.g. a 'find' box), they maintain relative position as you drag the main window across screens. Which, if you move to a smaller screen, puts them in offscreen no-man's-land where they can't actually be used or closed.
- Popups should consistently happen on either the active screen, or the active/furthest-forward window of the spawning program. As is, they unpredictably follow either rule, or borrow from the next bullet:
- Spotlight should appear somewhere sane and predictable. Either the same every time, or over my active window, or over my mouse cursor. Instead, it appears on the window which my Dock has most recently minimized to. My hidden Dock, which I have to use the mouse to locate/move. And then let re-minimize, because OS X doesn't update Spotlight's target when it appears but when it goes away. And which can automatically move itself to different screens without my help, based on where I open programs. Again, invisibly because it's hidden.
- And Spotlight's screen is also the screen where it will open new programs (a good decision). So I can't just look for it, I have to revert to the mouse to move either Dock or program to the screen I've been attempting to use this entire time.
So rambling aside, I think OS X actively causes time-consuming problems for multi-monitor users. I resent that because it's a pain even if I memorize the rules and how to solve the problems.
In particular, I object to tying large swathes of behavior to the Dock, since it's location/contents are both invisible and unpredictable for many users.
I think Apple was good at keeping things consistent across apps, but the chosen metaphors were sometimes just as confusing (if worse) than the blessed windows one.
Not that it matters, everything is learned behaviour anyways. Consistency is already a great achievement.