Feedback post on Overflow

Overflows can be connected to the perforated underdrain, or as a separate pipe that connects to the sewer system. The former may allow fine sediment, mulch, plant matter and debris to enter the underdrain, causing accumulation over time. The separate solid pipe is therefore often preferred, although more costly because more pipes are needed. Please comment on best practice - advantages/disadvantages. Clearly the larger overflow grates in the diagram above would have separate conveyance, but the smaller honeycomb overflows may or may not.