Step 1: Understanding the Concept:
Multiplying a complex number by $i$ rotates it by $90^\circ$, so $z$ and $iz$ are perpendicular and have the same magnitude.
Step 2: Detailed Explanation:
$|z| = |iz|$ and they are perpendicular. The triangle with vertices at $0$, $z$, $iz$ is a right-angled isosceles triangle.
Area $= \dfrac{1}{2} \times |z| \times |iz| = \dfrac{1}{2}|z|^2$.
Step 3: Final Answer:
Area $= \dfrac{1}{2}|z|^2$.