Hi Erin,
A sales available campaign is essentially a campaign that your sales folks can call on from salesforce. Publish to salesinsight typically refers to Emails not campaigns to make them available via sales insight.
So to be clear:
Sales available campaign****** Good candidate for nurture campaigns that sales folks can add leads to. For example, client's contract with competitor is active for 6 months ...add them to a 6 month nurture.
Publish to Salesinsight = Emails *****Good candidate for promotions like invitations to Dreamforce or Your user Summit.
Thanks,
Maneeza