The reason for the lights off nearing the end of your harvest deals with hormones. Flowering, and thus THC, will not be produced without a certain hormone present in the plant. This hormone breaks down rapidly in the presence of light, so the dark period is when the hormone builds up, and the plant prepares for the daytime to produce THC (trichromes are a light filter, specifically targeting high-energy UV radiation for THC production.)
That being said, without the light, you're not going to produce any extra THC, so leaving it in the dark logically doesn't make sense. You may be able to help with the taste because during the dark period all the nutrients are moved to the roots, where the plant then converts them into energy for growth, so there's less of a chemical taste in the actual plant matter.