Yes, internal links are important for a number of reasons. First of all you need to understand that for web crawlers like Googlebot links are comparable to flights into a destination. Web crawlers use links to get from one web page to another, so think about it this way, how easy is it to get to New York City by airplane. Now think about how easy it is to get to Fort Dodge Iowa (population 20,000) via airplane. If you make a page within your website difficult for the web crawlers to get to, they’re not going to travel there that often. For that reason alone you need to put a little thought into your website’s internal linking structure.
Secondly search engines look to link popularity within internal site link structure to tell them how important publishers think a specific area of the site is. In their view a page that can be reached through the site’s global navigation page is more important than one which can only be reached after 6 or 7 clicks, and should be treated as such.
There are additional reasons why internal link structure is important, but these are two of the biggest.