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For most couples I think the answer is NO. If you are happily married, live together and have otherwise clean backgrounds you should not need a lawyer for this process. It can be time-consuming and detail-oriented, but most English speakers will be fine. If this describes your situation, a lawyer can be more of a helpful luxury than a necessity.
However, some cases are complex. Some of you are divorced or are in abusive relationships. You will need waivers to get your I-751 approved. These waivers invite increased scrutiny from USCIS, need more detailed evidence and benefit from persuasive advocacy to win approval. Mistakes at this stage can land a person in removal proceedings. It’s much better (less expensive & less risky) to get it right the first time than to get help to clean up a mistake later. These are the cases where a good attorney can provide real value.