What is the primary benefit of underground detention with controlled discharge to a waterway?

Comprehensive and Detailed Explanation From Exact Extract:

Underground detention systems store stormwater beneath the surface, reducing runoff rates by releasing water slowly to waterways. The primary benefit is that they minimize surface land use for detention basins, thereby maximizing the developable site area available for buildings and landscaping.

Groundwater purity protection (A) is managed by treatment practices but is not the primary benefit of detention.

Site improvement costs (C) may increase due to system complexity.

Creating wetlands (D) relates to retention basins, not underground detention.