Design refresh includes updating the look & feel of your site, but also making sure that your site is current behind-the-scenes as well. For example, as new mobile devices come on the market and screen sizes in general change, adjustments to image sizes, font sizes, or other minor layout issues might be best. I design sites that work flexibly on a very wide spectrum of screen sizes, so I find the 24 month schedule is well suited to keep sites looking their best.