My salespeople come in and look at salesforce in their leads tab, either as "my leads" or "my open leads." They need to know more than the lead source (for us this is categories like trade show, website, white paper) they need to know that it was a specific white paper or trade show. I know it seems like they should be able to open the lead record and look down at the campaign window but since they have a lot of open leads, they are probably going to prioritize based on the campaigns where they feel the leads are most qualified (like someone who went to the trouble to download a white paper).