Page load speed is one of the many factors in the Google ranking algorithm.  In addition to this, the load speed affects the user experience and therefore it is important to optimize the load speed in order to promote the site.

There are many factors that affect load speed, these include:

• Image sizes
• Scripts loaded (e.g. JavaScript)
• Applications
• Redirects
• Page content (amount)
• Speed of the databases feeding the site

There are some fundamental principles that should be taken into consideration when setting up a website in order to ensure that the page speed is optimised:

1. Avoid unnecessary redirects - in particular leaving off the end slash on a URL forces a redirect to the directory that has a slash
2. Avoid 404 (page not found) redirects - make sure that there are no obsolete links on the page
3. Optimise the size of images on the page - as the screen operates at 72ppi it is unncessary to present images with higher resolution and images should be scaled to final display size 
4. Split pages when the content becomes too long
5. Compress scripts

Clinton Dickerson on Google+