Let's talk about Dabi's arms—not from any specific 'MHA' context, I'm assuming the question means abilities that involve arm augmentation or transformation, like 'armament' or 'demon arms' in fantasy series. The enhancement usually boils down to a dramatic shift in a character's physical and tactical options.
In a lot of shonen or xianxia, an empowered arm isn't just a stronger punch. It often comes with a unique energy system attached—channeling magic, ki, or curse power directly through the limb allows for concentrated, overwhelming attacks that bypass conventional defense. Think of it as having a built-for-combat module grafted onto your body; the user can switch from delicate tasks to devastating blows instantly, which fundamentally alters their engagement range.
What I find more interesting is the psychological and strategic cost. That arm often has a will of its own, drains the user's life force, or visibly marks them as 'other.' It forces characters to rely on a power they might fear or resent, adding tension to every fight. The combat skill isn't just about higher damage output—it's about mastering a double-edged weapon that changes how they see themselves in battle.