In English, when ordering food, you'd say "I would like x," not "Please let me purchase x," even though both are grammatically correct. You can say that "I would be liking x" is grammatically incorrect, is there a similar list of "rules" you can use to describe why "Please let me purchase x" is "incorrect"? I imagine this would be important in the study of dead languages?
The difference that you seem to be getting at is the difference between "grammatically allowed" versus "that's how we typically say things", i.e. style. Linguistics focuses mainly on grammar i.e. the sharper divide between possible and impossible. You have some chance of being able to distinguish grammatical from ungrammatical since that changes less frequently. Stylistically less-common on the other hand changes every year or so. "Doing+N"-constructions in place of more specific construction verb + N have dramatically risen in frequency over the past 20 years, e.g. "I'm making a Waldorf salad" (future tense) → "I'm doing a Waldorf salad". Once you become aware of some new construction like that, or the "is all" and "is, like" constructions, you can try to trace their frequency, which is more possible now thanks to our friend Google.