Seats and couches (sayana) are types of furniture used for sitting or reclining on. The last of the eight Precepts and the ninth of the ten Precepts say that one should abstain from using high (uccà) or large (mahà) seats and couches.
Some people are perplexed by this rule and wonder what it has to do with morality or the training of the mind. Of course it has nothing to do with morality. Only the first five Precepts pertain to moral behaviour and are kammically significant. The other Precepts, including the one about seats and couches, are ways of behaving that can assist in calming the mind and shaping character. In ancient India, and even in the modern world, sitting on an elevated or grand chair was a sign of power and status. Monarchs, judges, lecturers, managing directors, the speaker of parliament etc, all have special high seats. To practice the eighth Precept is to relinquish, not display or take advantage of one’s social status, at least for a day. Practicing the eighth Precept is about modesty, diminishing the ego and refraining from ‘putting oneself on a pedestal.’
- http://www.BuddhismA2Z.com/ Buddhism A to Z. Ven. Dhammika, 2007.