Snippets and Dynamic Content

I am having trouble with my snippets and dynamic content. I created a segmentation of all my lead owners, then I created a smart list for each owner, then approved them all.  Then I created snippets for each lead owner and approved them.  When I go to add the content to my email, I can either "replace with snippet" or "segment by".  Here I thought I would have to click replace with snippet but it only allows me to select one snippet, so I tried to do segment by but nothing changes when I go to the preview mode and go through the different emails, it registers that there shold be different emails but it does show my content.  Am I missing something?