I am working on http://urbantrend.co.in/test/ project. And In sidebar on category pages compare products disappears if there is no product http://urbantrend.co.in/test/index.php/womens.html. If i have some products in compare then that block will appear.
Kishor,your compare product block is render every time at category page ,but on that block's class template file,you may have a condition which is show block block-list block-compare block whenever you have any product in compare.
Basically this template file location may be
app/design/frontent/Your_Package/Your_theme/tempate/catalog/product/compare/sidebar.phtml.may on this file you have a condition like:
<?php if ($_items): ?> <div class="block block-list block-compare">