Business lead generation. Give the reader a taste of the content and have them fill out their info to get access to the entire report. Then you build a list that you can market to later. Hubspot does this well - http://www.hubspot.com/marketing-resources.

As a rule of thumb nowadays content should be more open and free to people. Use it to be recognized as an expert in the field and generate business that way. It is increasingly difficult for someone to "steal" or plagiarize work so I'm not sure you need to be so on top of protecting content that you miss bigger opportunities.