If you have a piece of content that requires a surrounding tag (like h2 around a heading, or p around the contents of a multi-line text field), you can use EnclosingTag on the FieldRenderer control; it will not display the enclosing tag if the field is empty:

<sc:FieldRenderer FieldName="Heading" EnclosingTag="h2" runat="server" />

Creates this:

<h2>My heading content</h2>

Strangely, it does not exist on the more specialised controls, like sc:Text or sc:Link.