Not necessarily. For example I might have a few gigs of photos to send someone, and I want to send them uncompressed. I could text someone the seed or QR code for them to download the photos, but I can't send those photos (especially uncompressed, even if over RCS or WhatsApp) over text.
Wouldn’t this use your internet data, though? Isn’t the point of these tools to send locally without being limited by internet speeds and without having to use your mobile data?
No, Iroh works over LAN as well.