7.6% of users visit from a search engine, while 22.3% via a hyperlink, and 70.1% come directly - i.e. You should not have too much external links on your website.Other wise this will affects your website negatively.That's why you should use alt tag on your all pictures, which you use in your website.
It's crucial to use alt tag and to make sure search engines know what you are talking about. Alexa rank is a scoring framework that measuring an activity and making characterization as per this movement those Alexa Toolbar clients are going to sites.
It is more important and beneficial for your site to have this at a lower value.