Sharing buttons help the lazy amoungst us tweet and post to Facebook far more easily – this in turns creates more traffic to your site, there are plugins for it but using the write implementation for your site actually will give you the best benefits. The information on it is here –
Using the available fields will actually increase followers too …
Authors should have their own branded twitter accounts and they should be in the first box, a second company account should also be in the related box
Two massive benefits, it will improve engagement with journalists who usually love it and secondly it will recommend following your primary Twitter account which is what you really want!
This is a bit more simple – http://developers.facebook.com/docs/reference/plugins/like/ – in the past there was a difference between posting to and liking, but very recently it has become the same, liking something will also post to their timeline.
Hope this helps