A high THC percentage in cannabis means a greater concentration of Tetrahydrocannabinol, leading to more potent psychoactive effects. This can result in a stronger "high," with more intense mood and perception changes. Conversely, a low THC percentage indicates milder effects, offering a more subtle alteration in mood and cognition, which can be preferable for those seeking less intense experiences or for medical users seeking therapeutic benefits without strong psychoactive effects.