If you've got a straightforward joint I-751 case (you're filing jointly and not requesting any type of waiver, there's no criminal history or other adverse factors involved, etc.), a lawyer usually isn't necessary. You might still want to hire one if you are just terrible with paperwork, or don't have the time to put into doing it yourself, but otherwise it's pretty manageable, and you can always get a lawyer involved later on if you get an RFE or otherwise feel like things are going south.
If you're really, really nervous about it and just want a second set of (professional) eyes to look things over, you could also ask your attorney if they would be willing to review it for the price of a consultation before you submit it. Not every attorney is willing to do that, but if you are an existing client (meaning they already know your case well and obviously know/believe you are a bona fide couple), there's a good chance they will agree.
TBoneTX is right about wills, medical powers of attorney, etc. As he pointed out on another thread, those things are also just good to have in general, as well as being good evidence of your lives together, so it's a win/win situation.
ahalow got a reaction from TBoneTX in Lawyer needed??? Conditions removal...