How important is internal linking?

I always try to internally link about 3 times in my posts making sure I try and link to every post I have made etc..

This is just for google though and making them understand my site?

You want to make sure that your main pages are linked from all your website page. If possible, install a drop down menu with listing of all your website pages.

Internal linking is very important. If you search post in download section which is about tutorial from chad on internal linking. He explained through internal linking you can earn better PR... although many people does not rely on that idea only but that shows importance of internal linking.