I will always disagree with using the main subs without a high pass filter as being universally better, especially with smaller mains. The distortion produced by smaller woofers in the lowest octaves is measurable and limits the overall dynamic range of the main speaker, ESPECIALLY with ported speakers. Plugging speakers used with subs can also further dramatically increase the available dynamic range of the mains.
If you are placing 4x12" or larger subs, then I can’t imagine most main speakers have much to contribute, besides distortion.
If all you care about is maximum bass dynamic range, with no thoughts given to distortion, I guess Geddes is correct. If you care about the entire dynamic range envelope then a high pass on the mains may be just the thing.