I think the point is that many "professional" tools have their own aesthetics independent of the rest of the OS. Things like lightroom or movie editing software. For these programs OS skins are not needed.
That's a very good point. That tool, however, should at the very least be internally consistent and pleasant to use.
I don't think that's what the person was saying that I responded to or he wouldn't have made the condescending remark about people using a pro machine to use Outlook and Facebook.
Not 'skins' per se, but even when themed, most (good) professional apps will still use native or native-behaving controls and similar design language to the host OS.
In comparison, Mac apps will look and feel different from Linux or Windows apps, and QT and GTK+ apps will look and feel different from one another or the other two.
Switching between apps, even with heavily customized UI/UX, is consistent on a given platform, and that's what's important. Taking that away will just frustrate users and complicate things overmuch.
Knowing how to copy and paste or which button to click to close a window is negligible when compared to the training required to properly use an ERP or even the most unique features of, say, Excel.
Anyone capable of navigating their way in Outlook can probably navigate their way in Apple's Mail or Thunderbird or Evolution. Anyone familiar with LibreOffice can do the basic stuff in Numbers in minutes.
Now, if you want a Notepad user to become proficient in Vi, that's a whole different story. Gedit, OTOH, is pretty easy.
Visual cohesion makes my day more productive because I spend less time mentally context switching between app philosophies.
Mental context switching is just like high CPU system time, with the same results. I/O is slower, user time processing is slower and much less gets done.
People will never stop complaining about look and feel. It's such a crap, it doesn't matter. How much clothes do you own? Computers are tools to do work and consume information, they don't exist for you to make a statement about your aesthetics opinions.
It's really nice that you feel that way, but I hope to hell I don't need to use software you designed. "Look and feel" and "Aesthetics" are core components of usable computer software, and consistency is the way you enable users to consistently use your software.
Setting aside the purely utilitarian aspect of being required to use a piece of software to do a task or as part of a job, consistency increases efficiency by reducing the amount of time spent understanding the deviations from expectation in the user interface.
To use your clothing analogy, consider this: what would you think if you bought a button up shirt and the buttons were not spaced equally, they were different sizes and colors, and some were on the right, some on the left. It works just as well as a shirt with standard construction, but it takes longer to put on and maybe it doesn't look very good.
There's been a great deal written about how attractive things work better. It isn't crap and it does matter.
Look and feel is more than just what colour an icon is, it's about how an application flows. Well designed applications enable you to be more productive, they usually also have had someone really think about what the experience should be as well which can help elevate them.
Who'd have thought it? People getting emotional about stuff.
When all software is designed to be consumed by other computers then we can ignore those emotional reactions, for as long as software is consumed by animals it is going to be a vitally important factor.
This alien concept (to many engineers) of beauty is a large part of makes new apps, especially web applications and SaaS startups, win or lose. Good design elements are the norm now, and expected. Gone are the days where someone would accept an ugly piece of solid software as a MVP. If it doesn't visually look as good as others in the ecosystem, your application is toast no matter how good it is otherwise.
That isn't true at all. I spend all day in a handful of applications and good aesthetics make my day much more enjoyable.