This. I can't test the staging area so I have zero interest in committing it. Actually I have less than zero interest; I would like my team to be prevented from ever creating untested commits.
If your workflow is that every commit must be tested, the correct approach is to enforce that rule, rather than banning an only tangentially related feature.
As for testing, it is trivial to stash or commit your current changes, go go the commit just made, test it, then carry on. A commit having been made partial only guarantees it wasn't tested if the developer is bad.
I commit the workspace. If I'm not happy with some of the workspace, I fix it (or stash it for later when chaos happens).
There's an inherent incompatibility between the supposed ways that the staging area can be replaced with other things. If you replace it with a commit you keep amending as you go, but also all commits must pass tests, then you can never commit partially complete code, which defeats the purpose of having the amending commit.
If you interactively choose what to commit at commit time, then you run the risk of failing the test and then, after fixing whatever was wrong, having to remember which parts of which files it was you chose to commit last time. Now, you could choose to have your CVS remember that for you, but then you're basically reinventing a less-capable version of the staging area.
If you simply commit everything, then you can never have any code in your working tree which breaks tests, nor can you have code which isn't logically part of the commit you're currently working on. In practice that means that when you find things that need fixing that aren't directly related to what you're doing, you either fix it and commit it with unrelated changes - which interacts poorly with merging or reverting those commits - or you don't fix it and, most probably, forget about it.
Other uses:
1. Breaking a large commit into multiple smaller commits.
2. As a simple "review" system. You stage files that have been reviewed so you know you don't have to look at them again, while continuing on a change.
3. Cleaning the working copy of superfluous changes/files. If you stage the files you want to keep, then clean and/or checkout force, it wipes out the files you didn't stage. Then just reset to unstage all files and continue making changes.
4. Splitting a branch into two different branches, when you realize that a branch could be broken down into smaller separate changes that are both incomplete, but COULD be committed separately. You merge squash to master, staging and commit creating a new branch for feature1, then stage, stash, and stash pop the rest back on to master (since sometimes you cannot just switch back to master), and create the feature2, and feature3 branches, etc.
I also use Magit in Emacs, which makes the staging area like the swiss army knife of Git. I cannot image the amount of extra pointless tedious work that would be required using commits, branches, and merges to simulate the equivalent behavior of the staging area. The staging area is used heavily by folks who like to get a lot of things done with minimal effort required.
I understand the difficulty for new users switching to Git, and I agree that the commands could be more clear and consistent, but beginner (commit all) and novice (selective commit) users should not be left to determine the utility of Git features they very likely do not fully understand or appreciate.
(How) does this work if you want/need a virtual paper trail of reviews and/or in a distributed team? Do you email your changes for review, without making a commit and push (to a branch and/or fork)? Apologies if I misunderstand what you mean, but I read "review" here as colleague walks by and have a look, and says lgtm?
Frankly, this demonstrates that you have exactly zero understanding of how git works. If I were the sort to force my team to do something, I would force them to never test uncommitted code. Committed /= pushed. A commit means you can keep working on the code while the tests run, and you won't forget what you actually tested. Then, when the tests come back clean, you won't accidentally push some additional, untested change along with the tested changes.
I do like the idea of having a snapshot of a test run, though we'd have to amend the commit or something to indicate that it passed its tests and is a sane parent for new commits on its branch, and I would switch to working on an independent feature rather than trying to do work on code which may or may not be broken.
This takes a really narrow view of what software projects can be hosted in git. If you're working on a huge project which must be built (at least for full builds) and tested "in the cloud", which you trigger by pushing to a temporary remote branch, then no, you need not have more than one workspace. If you're a webdev, then yeah, gitless or any other git workflow without the staging area might be useful for you.
Trying to use some other arcane or error-prone mechanism for getting changes onto test machines is exactly what will leak bad code, because inevitably people will end up sending around zips full of code from who-knows-where for who-knows-which-change.
If you're making an efficiency argument, git doesn't really try to beat the rsync algorithm even if you ignore the metadata. If you're making a "some people know git and nothing else" argument, fix the team, because that's a serious deficiency.
You're a bit confused about the difference between "concept" and "implementation". There's multiple ways to conceptualize git, but the one I offered is the one presented by the default porcelain while the one you offered is closer to the implementation. The encoding used for storage is entirely irrelevant to my point.
Anyways, my point had nothing to do with efficiency but was related to the topic at hand; that is, whether it it safe to use git to put code on test machines, and indeed whether that's safer than the alternatives. Nothing you said really addresses that point.