When purpose returns to the subject of comparison, the speaker aims to clarify, measure, establish, strengthen or colour an attribute of that subject. For example, likening a courageous person to a lion ordinarily intensifies our sense of the person's bravery.
In another kind of comparison, the purpose returns to the comparison term: the apparently subordinate image may be treated as the point of interest and presented as more excellent, prominent or memorable. Reversed simile is an important instance of this strategy.
The first direction includes explaining possibility, condition and degree, reinforcing an existing quality, beautification, disfigurement and making something unusual. The second includes reversal and emphasising the comparison term. Identifying the intended direction requires reading the praise, criticism and communicative aim of the utterance.