Check out this article from Dolby, which explains what an LFE track is. The subwoofer will reproduce LFE track audio and any other channel audio below the crossover points set. If speakers are set to large, that will send full range audio to those speakers, and with the crossover deactivated, no other channel audio will be steered to the sub(s). If all speakers were set to large, they would all be receiving full range and no signal would be steered from the other channels. All you would get is the LFE track audio reproduced by the sub.

https://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/38_LFE.pdf

What confuses most people is, how soon the loudness or gain an absolute volume circuit reaches reference levels, from the minimum or silent position, compared with a relative volume circuit, that will reach reference levels and possibly an additional 20dB of gain, max.
Which means, if the maximum range is 0dB on the control, reference level would be -20dB on the scale.
Sound and Vision has a fairly good explanation...

https://www.soundandvision.com/content/%E2%80%98relative%E2%80%99-vs-%E2%80%98absolute%E2%80%99-volume-what%E2%80%99s-difference