Hi Danial
Just in case you are looking of use cases for shared sets, here are some below:
1. Adding search queries. If you have an automated system that adds search queries, you can't compare them with negative keyword lists to see if they match. This currently means holding lists in two places which could become unsynchronised. The strategy we currently use is to apply identical negative keywords to every campaign as the overhead of manually managing negative keyword lists and their application to campaign is too labour intensive. The drawback of this strategy is that the client has hundreds of thousands of negative keywords and it takes an age to sync the account with AdWords Editor.
2. Apply list based on label (name match). Because it's hard to see at a glance from the AdWords campaign interface which lists are applied where, you could write an app (or script) which scans labels to see if any match the name of a negative keyword list. If they do and the list is not already applied to the campaign, apply the negative list to the campaign. Since labels can be viewed easily by customising columns in the AdWords interface, it's much easier to see which campaigns have which list applied.
3. Apply list based on label (brand). This is similar to above, but this time a specific brand negative list is applied if a "Brand" label is NOT attached to the campaign. This ensures all your brand traffic goes to your brand campaigns.
4. List "layering". This allows for additional negative keyword lists to be applied if the budget is being exhausted too quickly. An app (or script) could apply a more strict negative keyword list to help slow spend. You could have multiple "layers" of lists that can be applied based on how much budget it left. This is preferable to lowering bids or pausing campaigns.
5. Audit application. An audit application that checks if you are applying best practice to an account can't see if/how you are using negatives as it has no visibiliy of shared lists.
I hope that helps build the case for API access to negative keyword lists!
Cheers
David