Short version: yes, it needs to be excluded.
The value of the attribute is irrelevant, as long as it is present, the box will be checked.
<input type="checkbox" name="Publish" value="true" checked />
This is valid in HTML5.
In XHTML, the attribute needed a value and the convention was checked="checked"
since values like "yes" or "true" implied that the opposites would uncheck the box, which is not true and would confuse beginners. Similar conventions were adopted for readonly="readonly"
and disabled="disabled"
.