How exactly do cylinder spells and effects “ignore obstructions” in their areas? Or what kinds of obstructions they can realistically ignore?

So, Spell descriptions on Area entry says:

When casting a cylinder-shaped spell, you select the spell’s point of origin. This point is the center of a horizontal circle, and the spell shoots down from the circle, filling a cylinder. A cylinder-shaped spell ignores any obstructions within its area.

I feel like "any" is a bit to strong claim for how it does actually work.

Could someone elaborate step-by-step, how do you actually target such a spell when there are:

  • a low wall in a spell’s area;
  • a wall, higher than the height of cylinder’s point of origin, selected by a caster;
  • ceiling above one of desireable "targets", but lower then a mentioned point of origin?

Should all of them really be ignored?