In a finished room the objection to surface trunking is rarely technical. It is that a square box on a wall looks like an afterthought, and the client who agreed to it in principle sees it differently once it is up.

A trapezoid profile sits at an angle so it reads as a moulding rather than as a duct, and a low profile section keeps the projection small enough that a skirting or architrave absorbs it visually. The cable capacity is smaller, which is the trade, but for a final circuit it is usually enough.

Arc floor trunking is the same argument applied to a crossing: a curved top lets a chair or a trolley ride over the cable instead of catching on it, which is what stops a temporary route becoming a trip hazard.