Most people think about parallelism on GMAT Sentence Correction the wrong way.
They worry too much about how to apply parallelism, and not enough about when to apply parallelism.
Parallelism only applies in 3 situations: lists, comparisons, and around conjunctions.
Lists are straightforward. You want to make sure your reader knows the things are connected. So you might say “I enjoy dancing, reading, and writing” or “I took my dog, my cat, and my fish to the veterinarian.”
In comparisons, we want to make it clear that we’re comparing like things. So, you might say “I enjoy dancing more than running” or “The blue house is taller than the red cabin”.
Conjunctions, meanwhile, are short linking words, like “and”, “or”, or “but”. As conjunctions already link words, phrases, and clauses, parallelism makes the links more clear. So you might say “I am deciding whether to be a doctor or a lawyer” or “I am deciding whether to practice medicine or law”.
Note that in all these cases, the purpose of parallelism is to link phrases and clauses. If you don’t want to link phrases and clauses, don’t make them parallel.
If you want additional information on parallelism, you should watch my Youtube video on parallelism.
You should also consider picking up my book on GMAT Sentence Correction.