D. T-shirt sizing is typically used in agile when estimating detailed requirements during sprint planning. T-shirt sizing is an estimation technique used in agile development that involves assigning t-shirt sizes (e.g. XS, S, M, L, XL) to user stories or other requirements based on their relative complexity or effort. This approach is often used during sprint planning to help teams estimate the level of effort required for each requirement and ensure that they can realistically commit to completing the work within the sprint timeframe. Option A (Rationalism), option B (Trading), and option C (Visioning) are not commonly used estimation techniques in agile development.

D is correct - T-Shirt sizing is incredibly common in agile sprint planning, whereas rationalism is not. Sprint planning estimation is done by the opposite of rationalism - empiricism, resulting in a T-shirt size to understand the complexity of the task.