@comfunc There are several ergonomic aspects to this process that aren't obvious at first blush.
One issue is app/website window size and aspect ratio. For example, if you are making a calendar app (or displaying a webpage of Google Calendar), the best thing is a square shaped window, of a smallish size. The square shape is for Month view, obviously, and the smaller size is because it doesn't hold that much data (unlike a document or a spreadsheet), and its more convenient if you can say, look at the email request for a meeting, whilst at the same time examining your calendar.
That's one of the reasons mobile platform apps are so cute: they can be made just the right size and shape for the job you're doing with them.
Another example is Whatsapp. If you want to type messages on your laptop using Whatsapp Web, you don't want to have a massive browser window open just for that one little job, which is probably going on concurrently with other, more heavy duty work, on the same laptop. So you want to create, on the laptop, your own version of Whatsapp web, in its own window, with a remembered size and shape commensurate with its role.
A 2nd issue is of consistency and workflow management. For example, Fastmail is a great mail provider, with their own mobile app for Android and iOS, but they don't have a Win10 or MacOS app. This means that you have to structure your workflow differently in the latter environments - you'll have to use a browser window, and possibly get your Fastmail work mixed up with a whole load of other crap you've got going on in that browser.
A 3rd issue, I touched on before, is of identity management. Suppose you are at work and you use Firefox for work browsing and Gmail for work email. But suppose you also want to organise a group football trip in your lunchbreak. If you browse to gmail, it will pick up your work identity. Sure, you can swap, but you may accidentally send a private email from your work identity, if you forget. Then you want to buy your group train tickets. If you go to TheTrainline.com it will automatically use your work identity if you've already logged in there to buy a work ticket. You can get around this issue problem by using one browser for work stuff and another browser for private stuff. But its even better if you have the ability to encapsulate a particular function in a browser session with an encoded URL. In that case, you can create a desktop app/tile called 'PrivateMail', or 'FootballTrips', and by clicking on that you know for sure you are going to be in the right place, with the right identity.
Anyway, so this suggestion may seem a bit abstract and inconsequential, but actually its ramifications are very great.