Let’s take a standard fantasy game for example. You plan for there to be a fair bit of fighting, since it is a fantasy game. Now, when deciding what your MC can do to beat someone in the fight, you have two options:
1: High variability. You let your MC pick between being good at swords, spears, staves, bows, daggers and magic. Now, when writing a fight scene, these weapons can be split into two variants. Hand to hand weapons (sword, spear, daggers, staves), distance (daggers, swords) and then in addition to that, magic, which is probably even more variable than all the weapons combined. Now, to write a scene when you have to take out a guard outside a a gate you have to consider the best way to do it with all those weapons.That means that every weapon will get only one(maybe two) options each, and since the player only picked one weapon that means that the player only has a very limited amount of choices in a fight (low complexity), even though he had a lot of variability when making his character.
2: High complexity. Now, let’s say we say that the player only have the ability to be good with a dagger. Extreme railroading, you are playing a thief, that is your weapon. That means you can allow for a lot of complexity when it comes to the actual fight scene. Let’s say you have the same guard at the gate. Will you throw your dagger from afar? Maybe try to bluff your way close to stab him in the guts? Sneak up and drop down behind him to cut his throat? All of those choices, which in turn could lead to new choices whether you succeed or not because they are also paired with other skills (like bluff or sneak). When you have low variability for things the MC can do, you have the space to really play around with what they do with those things.
I see a lot of WIPS go overboard with early variability to try to please everyone, and then ending up with little complexity as the game progresses.