Final answer:
The part of speech that doesn't typically add grammatical value to a sentence is the interjection.
Step-by-step explanation:
The part of speech that typically doesn't add grammatical value to a sentence is the interjection. Interjections are words or phrases that express emotions or reactions, such as 'wow' or 'ouch'. They are not necessary for the grammatical structure of a sentence, but simply add extra meaning or emphasis. For example, in the sentence 'Wow, what a beautiful sunset!', the interjection 'wow' doesn't change the grammatical structure, but expresses the speaker's feelings.
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