A poet's choice of the words which they use in their poetry is of the utmost importance. Poems, given that they are, typically, much shorter that other texts, need precise words in order for the poet to convey meaning. The words chosen are important based upon the fact that they are used to convey certain images.
Images are used to elicit specific emotions and appeal to specific senses in a reader. Imagery, therefore, is important if the reader is to be able to connect to the poem. Imagery is used to appeal to the sense of sound, sight, touch, taste, and smell.
The best poets choose words which allow readers to create a mental picture. For example, in the poem "Eating a Mango Over the Kitchen Sink" (by Phebe Hanson), all of the senses of the reader are appealed to.
But a mango is a different story, impossible to eat except leaning
over the sink, tropical juice dripping down my pale Minnesota
winter wrists as I gaze
out at snow raging against my windows, like the storms of my childhood.
Here, the poet's word choice greatly affects the imagery in the poem. The senses of the reader are "attacked" on many different levels.
1. "Tropical juices dripping" appeals to both sight and sound. One can "see" (either through a vivid mental picture or a memory) juice dripping down one's chin. The juices then hit the sink face and make a sound--which appeals to sound.
This image can also appeal to the sense of taste. A person who has eaten a mango can use the words of the poem to remember how the mango tasted.
One can also imagine, regardless of experience with mangoes, the feeling of a fruit's juices dripping down their hands or wrist.
2. The "snow raging against my window" does limit some engagement by some readers. Not everyone is familiar with snow, let alone Minnesota snow. This line (word choice) could alienate some readers given that they do not have experience with which to relate it to. The word choice here could cause some readers to lose interest.
The image of "storms of my childhood" works in the same way. Some readers may not be able to relate to the allusion of a bad childhood. Others may read the line for face value and take the image literally--meaning actual storms during their childhood.
Therefore, in the end, word choice has a great effect on the imagery and the engagement of the reader.