A regular website maintenance is essential, to ensure that your site is running without disruption and performed as expected.
All Webhosting Providers are doing cyclic backup for their servers, and they provide a control panel where you can download those backup files.
However, you should do your own backup to your local computer, especially every time you made changes to the site, or use Online Backup services.
Without that backup, if something happens to the server such as server down, or hacked, you will lose your last editing; it will be gone. In an emergency situation where your web server down, you're able to rebuild your website with other providers if you have a backup.
In general, search engines robot will index hundreds of millions of pages, and respond to tens of millions of queries per day. If you never update your website, you will not get ranked in SERP (Search Engine Result Pages), or even, it might not be listed at all.
If you want to get listed and ranked by Search Engines, website pages required a regular update, especially your Homepage and Landing Pages. It doesn't mean that you should change the overall content of each page. Rephrase or new keywords will work as long as the changes still relevant to the page content.
If you're working with a Copywriter /Online Marketing for your website project, you will have a library of keywords, slogans, content titles, and headlines. You can re-use them to update your pages without changing the overall context of your content.
To make changes, or add a new page to your website, you can do it using CMS. Most of CMS (Content Management System) are user-friendly, easy to use by average users. However, as a business person, it will be good for you to focus on your business and let a webmaster do that job for you.
Site Traffic Monitoring & Report
Site Analytics is an online tool to analyze your website traffics and statistics.
Your website contains different applications, plug-ins, and third party API (Application Programming Interface) that sometimes required a regular software upgrade. A Webmaster role is important here to ensure that your website applications are always up to date following the guidelines from each software vendor.