Hi.
Let me give some thoughts on the Pirc-Modern complex, as some set of lines from this is what I usually play against 1...e4.
To begin with. There are unique lines to the Pirc (1.e4 d6 2.d4 Nf6 3.Nc3 g6) and unique lines in the Modern (1.e4 g6). Not to mention multiple, multiple side setups like the Czech (1.e4 d6 2.d4 Nf6 3.Nc3 c6) or the North Sea (1.e4 g6 2.d4 Nf6) that I will not exactly touch on. I'm not exactly sure at this point what you learn in the Pirc and not in the Modern though and vice-versa so I will still present as the Pirc-Modern complex and not each individually.
In the Pirc-Modern complex I'd say one learns things like:
- Playing against flexible central pawn formations (not fixed like in some other openings)
- Timing pawn moves that go beyond the 6th rank (or white can often make these pawns into targets)
- Colour complex play (Usually black has quite good conditions to be strong on the dark squares and so quite often situations where black plays heavily on these occur)
- Coordinating development (not much space to develop to begin with and sometimes certain developments are sensitive to white thrusts)
- Playing with the queen (it's often used as a supporting piece for central play or as active punisher for overextended white positions)
- Attack/defense of the king (Many direct attacking lines that easily can end up targeting the black king exist. It's harder to get king attacks as black but can happen as well)
- Playing for and with queenside space (If black gets in b7-b5, as usually happens, the pawn can stay there for a long time in many positions and sometimes threaten to advance)
- Material for initiative positions (Basically white can often go a bit wild and sacrifice stuff in these types of openings)
- Double fianchetto positions (so having both g7 and b7 bishops, it happens, but is not completely common in many other openings. Especially e4 ones I would say)