This is a special place where you can add almost any text you want, like a small biography, an introduction to your blog or site, some links or even some ads, almost anything remember. Another good idea is to use this space as a section for announcements and news, that way your readers will nkow what's coming in your blog! Just be creative.
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Oh! And don't worry about the space and the size, this is an expandable sidebar within the sidebar! So you can just keep adding more and more content!