Macrojack, similar to the newer WPs, my Merlin VMXs are measureably flat +/-3db to 30Hz and produce usable bass down to 25Hz. Adding a sub below a low 30Hz crossover point adds significantly to impact of kick-drum, electric and acoustic bass, and expands the acoustic space for other instruments that unexpectedly reveal content well below 30Hz to a spectrum analyzer. It's also a nice dividend that at such a low crossover point, the transition from sub to mains can be smooth & unobstrusive, even moving from a hi-watt SS sub amp to a tube amp on top.
Since the human ear attenuates bass response as volume decreases, it's nice with a sub to be able to control volume & add a little boost as needed. Deep bass response of most rooms is tricky enough that being able to relocate the sub-bass woofer away from the main speakers can be an advantage. And all other things being equal, it's a lot cheaper to match a fine sub with fine limited low-frequency main speakers, than to acquire large-array full-range main speakers of comparable quality.
Finally, any additional tweaking required for a sub is a satisfyingly visceral exercise relative to wanking over power cords.
Since the human ear attenuates bass response as volume decreases, it's nice with a sub to be able to control volume & add a little boost as needed. Deep bass response of most rooms is tricky enough that being able to relocate the sub-bass woofer away from the main speakers can be an advantage. And all other things being equal, it's a lot cheaper to match a fine sub with fine limited low-frequency main speakers, than to acquire large-array full-range main speakers of comparable quality.
Finally, any additional tweaking required for a sub is a satisfyingly visceral exercise relative to wanking over power cords.