Not only tag, but list, smart list, contact, location.

They are convinient and many these items made and used.
On Mac desktop app or Web app, many many these items don't make to be inconvinient.
But on iPhone app, display is too small to see many many these items, then I have to use fewer items than I want to use.

I suggest that these items (tag, locatoin, etc.) can be set to visible or invisible on iPhone app.