Facebook SDK & Using Social Plugins? - facebook

Question

I originally posted this question on the FB Developer forums, but received no response...so figured someone here might be able to help.
When using the FB Social Plugins I have seen several articles outlining the following code (this is just a general example as the fb:like attributes can vary of course):
Code:
<div id="fb-root"></div>
<script>
window.fbAsyncInit = function() {
FB.init({
appId: '#############', //configure FB App ID
status: true,
cookie: true,
xfbml: true
});
};
(function() {
var e = document.createElement('script');
e.type = 'text/javascript';
e.src = document.location.protocol + '//connect.facebook.net/en_US/all.js';
e.async = true;
document.getElementById('fb-root').appendChild(e);
}());
</script>
<script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script>
<fb:like href="www.domain.com" show_faces="false" width="450" font="arial"></fb:like>
I am wondering the following:
1) When using most of the social plugins (Ex: Like, Activity, Recommendations, etc) is there a need to include both the full SDK script and the second script tag?
In other words could one just include the following on their site:
Code:
<script src="http://connect.facebook.net/en_US/all.js#xfbml=1"></script>
<fb:like href="www.domain.com" show_faces="false" width="450" font="arial"></fb:like>
2) Are there any advantages of including both?
3) If you do not include the full script is there any reason to register for an App ID?
Thanks for any clarification that you may be able to provide!