Yeah I know I know, I made a meta example about the problem, but can happen to everyone.
Tzeentch's endless spell became a core part of their book, if you don't have them, you can't play it at 100%. Chalice in FeC unlocked a new way of building a list, same with stormcast and meteor or Nh with the auto-cast; Sylvaneth needed theirs until the release of belthanos (and still take it), Khorne needs all of them, same as Fyreslayers. You are going to feel that your list is missing something.
With sceneries is even worse. Is impossible to play without scenery in Gloomspite, BoC, Sylvaneth or Nurgle, is a big hit in your list for idoneth, khorne or ogors.
They are such a integral part of some strategies/armies/playstyles that the lack of stock causes frustration.