When an application raises a window, it becomes active, and if the user is typing something at the moment, the typed data is lost. I find this very annoying. Window manager should not raise windows when user is actively typing something, or there are buttons held pressed. Back in X11, there was an 'focus-stealing prevention', that among other, X11-specific things did not let the activating window to interrupt your keyboard input.
Real-life case: Konsole & Steam After a reboot Steam takes a while to start, and while it loads I used to switch to Konsole and type commands I need. But during startup, Steam opens up to 5 windows with a notable delay. In X11 session it is no problem, Seam windows are opened in the background as I type. But on Wayland Plasma session, EACH time Steam opens a window it comes into focus, interrupting my Konsole input. This should not happen. Same applies to many applications that do some kind of a long-running work, and make a popup in the end. However, if the raise request comes from the application that owns currently active window, it should not bring it up like usual, e.g. when you're working in a text editor and press Ctrl+F to bring up a search window.
*** This bug has been marked as a duplicate of bug 364689 ***