Spellcasters do not always need to provide the literal materials when casting spells with costless components, that's what pouches and foci are for.
A character can use a component pouch or a spellcasting focus (found in “Equipment”) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.
However, there are a handful of spells that have consumed materials without a cost, such as:
- Globe of Invulnerability (Glass/crystal bead; consumed)
- Snare (25ft of rope; consumed)
- Create Homunculus (Clay, ash, mandrake root; consumed, 1000gp jewel-encrusted dagger)
- Druid Grove (Mistletoe harvested with golden sickle under full moon light; consumed)
and we have the following blurb:
If a spell states that a material component is consumed by the spell, the caster must provide this component for each casting of the spell.
Can a Spell Focus or Component Pouch substitute components with no listed cost if those materials are consumed by the spell?
RAI: They are consumed
Because there are three places that talk about consumables, foci and pouches, and they seem to disagree, we must look to the intent of the game designers. When Asked:
Jeremy Crawford replied:
And here again, Jeremy Crawford states:
So, the rules as intended by the designer is that they are consumed, and the pouch doesn't just have an endless supply of these consumables. He did add:
So, a generous DM can run this the other way, without breaking balance. Items with cost, however, could break balance.