In the game Aidyn Chronicles: The First Mage, one of the close friends to the character you play is an NPC who's a reluctant knight. Though the knight has sworn off the violence of battle, he's continuously forced to fight for his king, both for his own honor, and to support a noble cause. He carries a pole bearing a flag or banner of the kingdom he serves. As a tool of gameplay, the banner has certain protective functions.
But it often gets ripped in battle symbolizing how the knight's heart is torn every time he violates his decision to abstain from fighting. Furthermore, the banner, when torn, prompts discussions by the knight and those around him as to the ethics of his fighting in battle versus being a man of peace. The banner is a Symbolic Subplot, indicating, at any given moment, where the knight stands as he wrestles with the difficult decision to be, or not to be, a warrior.
This is one of those examples where a symbol serves double duty. Not only does it deepen the emotional experience, but it also is a Usable Symbol with a function in gameplay.
Does this Symbolic Subplot deepen the emotion of the game? That all depends on whether you feel that, as your character grows and changes, you, the player, are also experiencing growth and change, at least to some degree.