Tier 2 links add extra power to tier 1 guest posts and niche edits. They are especially recommended for new guest posts which will have no inbound external links when they are first created.
They are also particularly good for powering up lower level guest posts and niche edits.
Tier 2 links are permanently placed on the homepages of high authority websites which are fairly relevant to the topic of the target page. We use generic contextual links within existing articles.