> while you won’t actually be able to see the part of the image under the sidebar, on the other hand the transparency effect applied to the sidebar will make the text on it less legible overall. A great lose-lose situation, visually, don’t you think?

Yes, of course, but it looks bold and innovative and designers can waste years tweaking various details across many apps!

> reduces the amount of information displayed on screen, and you’ll have to scroll more as a consequence. ... You’re just injecting white space everywhere.

Sure, but that's a common scourge in all modern design, why would an innovative design company stay behind?