I use a lot of dummy texts in my template to see what the page will actually look like when rendered. To filter out these fragments I created a "Dummy" component whose setupRender method always returns "false".
I don't know if this is efficient but it would be nice to have something like this already in T5's component library.
More efficient would be a special marker XML attribute that the template parser recognizes. Maybe something like a t:test attribute which is works like <t:if test="...">...</t:if>. If the contained expression evaluations to false or null the marked element is filtered.
<li t:test="show.item">conditional item</li>
<li t:test="literal:false">dummy item</li>