I would advise against it!
Backing up your data on regular intervals is utmost necessary. But if you are taking backup on a hard drive, then that might be risky. There are high chances of your hard drive getting damaged or even erased.
So while there is no harm in backing up your data to hard drive, it should not be the only option. Since data can be lost from here as well, it is always better to go for multiple options of storing your website data, only to be on a safer side. You can store your data remotely as well on 2-3 locations, such as Google Drive, Dropbox, etc.
But even if you have stored your data on Hard Drive alone, and your drive crashes, then you can go for Hard Drive recovery as well. Although it is a costly process, but your data would be back to you safe and sound.
Otherwise, you can go for online backups, which can be done using some popular plugins if you are using WordPress.
This is the highest ranking backup plugin for WordPress. More than 1 Million people are already using this plugin for keeping their content safe. It highly simplifies your backup and restoration process. Using this, you can quickly backup your content to cloud storage. And when required, you can restore the content with just a single click.
Today, more than hard drive backup, cloud backup is coming into play. AWS migration has become very common ever since Amazon launched its cloud for the people. So plan your backup on cloud regularly.
This is another reliable plugin which would keep your WordPress content safe. All the websites are prone to hacks. Hard Drive is prone to getting crashed. So in such a case, having a backup is extremely helpful option. Backup Buddy is one of the best plugins that will assist you in this task.
This plugin allows you to automatically create backups of your complete WordPress site and save them on multiple remote locations. These locations can be your computer, storage server, FTP server, etc.