Having asked this question previously, I do know what s'agir means, somewhat. However, it seems to me that I most often see it used in a way that in English would translate directly to "It's..."
This leads me to be uncertain as to how it differs from simply using C'est...
For instance, what is the difference between the following two sentences?
Il s'agit d'une pièce à deux personnages.
C'est une pièce à deux personnages.
I would think both mean "It's a play with two people."
Likewise, here are two more:
Il s'agissait en effet de Drago Malefoy.
C'était en effet Drago Malefoy.
How do these differ? Are there certain contexts where Il s'agit de... is simply more appropriate, like when describing the content of something, what it consists of?