added some more information on the spaceless tag documentation

doc/tags/spaceless.rst

@@ -1,7 +1,8 @@
 ``spaceless``
 =============
 
-Use the ``spaceless`` tag to remove whitespace *between HTML tags*:
+Use the ``spaceless`` tag to remove whitespace *between HTML tags*, not
+whitespace within HTML tags or whitespace in plain text:
 
 .. code-block:: jinja
 
@@ -12,3 +13,25 @@ Use the ``spaceless`` tag to remove whitespace *between HTML tags*:
     {% endspaceless %}
 
     {# output will be <div><strong>foo</strong></div> #}
+
+This tag is not meant to "optimize" the size of the generated HTML content but
+merely to avoid extra whitespace between HTML tags to avoid browser rendering
+quirks under some circumstances.
+
+.. tip::
+
+    If you want to optimize the size of the generated HTML content, gzip
+    compress the output instead.
+
+.. tip::
+
+    If you want to create a tag that actually removes all extra whitespace in
+    an HTML string, be warned that this is not as easy as it seems to be
+    (think of ``textarea`` or ``pre`` tags for instance). Using a third-party
+    library like Tidy is probably a better idea.
+
+.. tip::
+
+    For more information on whitespace control, read the
+    :doc:`dedicated</templates>` section of the documentation and learn how
+    you can also use the whitespace control modifier on your tags.