Some cardeffects say "When ..., You can" in their effects. An example, Gusto Falco:
When this face-up card on the field is sent to the Graveyard, except by battle: You can Special Summon 1 "Gusto" monster from your Deck in face-down Defense Position.
This means that it has to be the last thing to have happened, for it's effect to be able to activate. Like by Torrential. If it were to be used as Synchro Material Monster, it'd miss timing, because the Summon of the Synchro Monster was the last thing that happened. Cards that say "If ..., you can" can be used, they simply start a new chain after the old one resolved.
