Lots of businesses go to the expense of having a website created but then once it is live, leave it to go stagnant. It is important to keep your website content and back end code up to date for a number of reason. Not only will your visitors like to read the most up to date information and see that your website is in line with your social media etc but also the search engines do. Website that have not been changed for months or years will find that they start to fall down the search engine rankings. This can mean that very quickly their site cannot be fund easily for their main search terms and they notice a drop in traffic. Drop in traffic also means less sales and enquiries.
With regards to the back end code, it is important that this is also kept up to date to ensure smooth functionality of the site but also to ensure that it is secure. Code that is outdated can often mean that a site can easily be hacked. This can cause a number of issues such as redirections to sites that are stelling identity information, change of content on your site or even ransom demands.