I know it doesn't have to be said for anyone already participating in this thread (who already know a great deal about Pacific Island kava culture), but for those unfamiliar, yaqona is consumed most commonly in Fiji and Tonga as a social lubricant. It's not very common for people to drink yaqona alone. In fact there is a little bit of a stigma around doing so (although it seems to be fading in urban areas).Drinking diluted kava doesn't have much of an effect for me.
If you want to spend the evening chilling with friends, shooting the breeze or having a sing-along with a guitar, then a sosoko mix (thick, strong yaqona) that puts everyone to sleep within an hour isn't ideal. Hence the preference for yaqona waicala (weak, diluted yaqona) that one can drink for hours.