During the period of The Book of Songs, poetry was very mature. Kings educate princes with poems, and nobles educate people with poems. In that era when words were still in the hands of a few people, poetry had already spread all over the world, relying on word of mouth. So the beauty of poetry is inevitable.
Metric style appeared in the late Wei, Jin, Southern and Northern Dynasties, and a large number of literati began to pursue the beauty of melody and the skillful use of words, which was basically finalized in the Tang Dynasty. This is the inevitable product of the development of phonology in a certain period. The poet summed up a complete set of even and flat metrical patterns, so that later scholars can easily write cadence and catchy poems by learning metrical knowledge.
Metrics is actually a set of tools for people who study metrical poetry. If you make good use of the doorway that can quickly enter ancient poetry, you can't go too far in terms of rules. If you can achieve a beautiful artistic conception and "do whatever you want without overstepping the bounds", then congratulations, you are already a master of poetry.
Poetry expresses ambition. After the appearance of metrical style in Tang Dynasty, many poets did not write poems according to metrical style. Why do you think of Tang poetry and metrical poetry when you say ancient poetry now? This is because of childhood education problems. In fact, if we make a big comb of China's ancient poems, we will find that no matter in which dynasty, the number of unqualified ancient poems is far greater than that of metrical poems. At the same time, Li Bai and Du Fu, Li Bai did not love metrical poems, but wrote ancient Wang Yang with unrestrained romantic fantasies. Du Fu is a master of metrical poetry. He is basically concerned about the country and the people, and his words are neat. Therefore, it is the "immortal" who shines, and the "saint" who makes rules and conforms to the law. However, this is based on the peerless talents of Li Bai and Du Fu.
The rhythm and balance of poetry are like a navigator when you enter a new field. After mastering it, it will tell you how to get there so as not to get lost and be laughed at. When you thoroughly understand this field, you naturally don't need to use it.
Another point. Poetry, because ancient and modern poetry, is not qualified to write. But if you want to write a word, don't learn the name of the epigraph and the inherent rhyme of each epigraph, then don't say that you wrote a word. Inscriptions are more rigorous than poems, so if you don't like to follow the rules, just write some ancient and modern poems.