Internet-routed media transfers, bypassing some (very) shitty filtering done by carriers. Most will compress and downscale any media sent via MMS. A friend didn’t have RCS until recently, and I always had to remember to send links and not actual pictures because they would always recieve unreadable garbage if I let the carrier transfer it. But really, ANY other messaging app solves this… Signal, Telegram, Discord, even Steam Chat will blow the pants off MMS.