Standard media applications install addon code directly onto your local device. This creates security risks and consumes local storage. Stremio addons are web services hosted on remote servers. When you install an addon, you are simply saving a URL manifest link to your account. Cross-Device Synchronization
Put simply, are content providers. They are the "channels" or "sources" that feed metadata, catalogues, and actual video streams into the Stremio interface.
Without addons, you only have the "Local Files" addon, which plays videos from your hard drive. With the right selection, you gain: