Cloud compressors upload your full file and store it on third-party servers — with leak, retention, and compliance risks. Local processing runs in device memory only: no upload, no server copy. For internal training, client demos, or family videos, local tools match privacy expectations. MBox also skips upload queues — many files finish faster than round-tripping to the cloud. Cloud still helps for very large files or weak devices; local wins for privacy-conscious everyday work within browser memory limits. Use both where each fits best.