My case is very straightforward. Other than 3 minor traffic tickets that are all over 7 years old I have nothing in my application that requires scrutiny. I arrived in a fiancee visa, got married, filed for GC, got GC and now I'm applying for citizenship, still married to the USC on the original fiancee visa.
Had I spent any time out of status, or switched statuses in an unusual way, or had some criminal history that was serious/recent enough to potentially be a problem, then I'd think about getting a lawyer.
If at any time I had done something that made me deportable then I'd DEFINITELY have a lawyer. (And would probably choose to not beomce a USC just so that I stay under the radar....)