Finally, even though we got here by discussing sound, note the stronger and more nuanced meaning of .
Not only are contractions fairly "weak" words, their expanded forms are rarely much better.
I once took a class where we were asked to never use any form of the verb "to be".
I learned a lot about writing style in a very short time.
In class, do what you are told so you can get good marks, graduate, get a good job, and be able to afford to buy good books which you can read to improve your taste.
In the larger picture, be aware that many so-called writing rules have nothing to do with effective communication.A conversational style can be appropriate for many kinds of writing, but developing the skills to write in other styles is at least helpful, and in some cases it's critical.I can think of three types of writing off the top of my head where attention to seemingly minor details, like contractions, is very important: lyric writing (poetry and song), dramatic dialog, and political speeches. Potentially all writing can be improved by attention to word choice, but details of word choice can be especially critical in these three categories.Tack on another two to seven metrically related syllables and repeat at least part of the line, and you've got the beginning of a song or persuasive speech.There is only one unvoiced consonant, /p/, and the stop there can be effective in strongly establishing the pattern of two trochees.Contractions share a few tonal qualities that can be problematic.Contractions are formed by eliminating vowel sounds and compressing two or more consonant morae into one syllable.In some cases, two or more unvoiced consonants are put together (e.g., ).Consonant clusters can slow down singing and speaking and also create phonological noise and ambiguity.This rule is because it is easier to impose simple rules than to inculcate good taste.In real life, try to develop good taste by reading excellent examples with attention.