The key is to not give it any agency over the work product but rather have it act as an editor or advisor that can offer suggestions but every thing that goes into the document is typed by human hands.
Giving it a document and asking it about edge cases or things that may be not covered in the document. Asking it for various ways that one could argue against a given pleading and then considering ways that those could be headed off before they could even be raised.
In my on cases (writing short fiction), having it act as an editor and identifying grammatical mistakes, contradictory statements, ambiguous sentences, and tone mismatch for a given character has been very helpful... but I don't have it write the short fiction for me.
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For software where it may be used to generate some material (write a short function that does...) the key is short. Something that I can verify and reason about without too much effort.
However, changes that are of the scope of hundreds of lines are exhausting to review no matter if an LLM or a junior dev wrote them. I would expect that similar things would be the case of several paragraphs or pages of legalese that would need additional levels of reading and reasoning and verifying.
If its too much to reason about and verify - its asking too much.
I'd no more trust an LLM to find citations to cases than I'd trust it to program a lesser known framework (where they've been notorious for hallucinating up functions that don't exist).