When is it preferable to use a square outlet box rather than an octagonal-shaped one?

Using a square outlet box is preferable when more space is needed because these boxes typically offer greater volume for wiring and connectors compared to octagonal-shaped boxes. Square boxes provide additional space to accommodate multiple wires or larger fittings, making them more suitable for applications where more electrical connections or a larger device (like heavier light fixtures) may be installed.

In contrast, octagonal boxes are usually designed for specific fixtures and may not provide the same volume or versatility. The decision should be based on the requirements of the installation, such as the number of wires or the size of the devices, where a square box can effectively meet those needs with its increased capacity.