Nobody likes a slow website - with the fast-paced world we live in, users don't have time to sit and wait for your website to load. The average size of a web page from the top 1,000 websites is now 1.62mb (http://www.websiteoptimization.com/speed/tweak/average-web-page/?ref=georgebuckingham.com).
When a user views a webpage, their web browser often needs to get a number of other resources (CSS, JavaScript, images, fonts etc).
Loading the JavaScript at the bottom of the page will ensure your content loads before any interactivity takes place.
By reducing the dimensions the file filesize will also reduce, leading to faster loading times and a reduction in bandwidth costs.