The Mac Pro and MacBook Air both ran the same software. There wasn't really anything more or less pro about either one except for the specs.
Because you need a minimum user base to make them work.
It's the same logic as how I can airdrop files or share notes with another iOS user, without needing to first check if they have said feature installed. Saves on a ton of unnecessary assumption and guesswork, which in turn helps ensure that said feature gets used more.
I find I can't really give a short answer to your question. I thought it was fairly straightforward, but the more I tried to verbalise my thoughts, the more convoluted it got. Here goes.
Terms like "beneficial" mean different things to different people.
You used the terms "efficient" and "more productive", which while being tangential with "beneficial", isn't necessarily analogous. You want your device to do more, and don't mind incurring more complexity for it. Apple makes it so that users can do more with less, or at least do the same thing with less.
Let's compare Pages and Word as an example. Pages has maybe like 10% of the features that Word has, but those are the 10% I really ever use. What I get in exchange for less functionality is a streamlined interface which is easier to navigate and more aesthetically pleasing. Now, "It just looks better" isn't a benefit which I can quantify into a numerical value the same way you argue "my app has 10 features over your 5", but it's one which has a positive impact on the way I use said app.
In addition, I find I don't experience many of the problems I traditionally faced with Word, such as formatting and alignment problems. I generally spend less time fighting Page's interface compared to Word, which results in less time wasted and improved productivity overall. I voluntarily gave up more functionality in exchange for fewer problems and headaches.
The end result is that while Word undeniably lets me "do more", I still find myself gravitating towards Pages whenever I can because it's what I prefer and what I am comfortable with. What Apple has done here is decide on a streamlined list of features which they feel are the most important to the end user and dump the rest. Unlike Microsoft who just dumps everything into their software and leave it to the consumer to sift through everything and figure them out on their own.
That's what I pay Apple to do - make the hard decisions for me as to what (they think) I need and don't need so I don't need to. Does Apple always make the right call? Not always, but they get it right enough times than not that I am content to sit back and let them call the shots in this regard.
Pick your poison, because you can't have both.
