Read more on why to use Zotero on the Zotero "Why Zotero?" webpage.

Learn more about Zotero storage here: https://www.zotero.org/storage?id=storage

There are also storage plans for labs and institutions you can check out. Zotero groups can also use Zotero Storage at no additional charge, except whatever is needed for the storage account of the group owner.

If you are interested in using WebDAV, here's a list of services which people have successfully used with Zotero: https://www.zotero.org/support/kb/webdav_services

If you are syncing using ZotFile and linked files, you can use something like Dropbox or Google Drive. Learn more here: https://www.zotero.org/support/sync