There are some cases where you won't be able to use portrait mode... like when it can't find a main subject. You might see the message "move closer" or "move farther away" when you try to shoot a landscape shot in portrait mode. There are a number of things you lose shooting in portrait mode:
No wide angle
No burst option
No Live photo
There may also be times when you want to take a photo of someone, but you want the background to be completely in focus. Of course the XS will let you control the amount of background blur (depth control), so maybe there isn't much to lose from shooting people with portrait mode. Portrait mode also gives you access to the studio lighting stuff. If it works for the stuff you shoot, keep using it. Just remember there are other options when it just isn't working for a particular shot.