Basic question about updating local.xml

I have a basic question that which way of updating is good in local.xml or in every .xml files separately. I observed that for each update i have to go to my .xml files in base then copying tags then edit. I already did a project editing .xml files separately from my local package/theme. It looks easy to me. I want your suggestions as i am newbie

I followed the link for better way of layout update from local.xml as well: http://classyllama.com/development/magento-development/the-bette开发者_JAVA百科r-way-to-modify-magento-layout/

Pros and cons of local.xml explained here http://inchoo.net/ecommerce/magento/using-local-xml-for-overriding-or-updating-xml-structure/