Shared negative lists are tempting when you have a dozen campaigns and the same junk terms (free, jobs, careers, "how to") turning up everywhere. Google lets you attach one list to many campaigns, so it looks like the obvious fix. The catch is that a list that's right for one campaign can quietly block a term you want in another. Say a SaaS company adds "pricing" as an account-level negative to cut cheap-intent noise, then can't work out why its comparison campaign has gone quiet.
A reasonable split is shared lists for terms that are never relevant anywhere, and per-campaign negatives for anything tied to intent. Does anyone run the opposite, one master list with explicit exceptions, and has it held up?