Keeping your website updated shows Google you're on the ball which is important as they want to promote websites they know their users will enjoy. Google check your website every few weeks, so having stale content with no change in months will hurt your SEO performance and show those who do still visit your website that you're not keeping it up to date.
Blogs with dates from 2 years before, or Merry Xmas messages showing in February hurt, so use our FREE changes policy and keep your site up to date always.