Network Attached Storage, can be an important addition to a network for a variety of reasons. NAS, is a small always-on computer generally used for backing up computers and serving files to devices on a local network. Unlike a USB drive or an external hard drive, a NAS with two or more hard drives can provide data redundancy, copying the contents of one drive over to the other automatically.
For both home and business levels, a NAS is great for large media libraries because you can store your files in one place and stream them locally to computers, phones, tablets, speakers, or media centers throughout the network. They can store photos, music files, and access large amounts of data from multiple computers. A business level NAS, can collaborate with iSCSI devices, SANs (storage area networks), or RAID configurations such as RAID 5, 6, or 10. You can even build a NAS with free software such as FreeNAS or XigmaNAS however, dedicated NAS devices uses far less power, have better software, often support Apple's Time Machine backup tool, and comes with a manufacturer warranty and technical support.
If you want to protect your data and backups from theft and natural disasters, a good NAS is capable of uploading files directly to a cloud backup service, such as Amazon Drive, BackBaze B2, Dropbox, Google Cloud Storage, Microsoft Azure, Open Stack Swift, and more.