It's true that if nobody you want to talk to is on it or willing to install it, then it's not of much use. It's also a bit harder to find really compelling features for direct messages. Though even for DMs, outside of Apple's walled iMessage garden, it's hard to get stuff like high quality photos, videos, and audio messages, reactions, stickers, etc that work correctly for everyone on all device types.

Group handling is where all of the apps really shine though. Doing groups in SMS is basically garbage compared to pretty much any chat app ever made.

Everyone keeps saying group. I've never had trouble sending group texts. Both my kids have had their whole classes in a group text for a year. SMS is the one and only "open" messaging platform left so your experience will depend on if you're using iMessage or Samsung or VZ or whatever other ones are out there. But as far as I can tell they're all perfectly fine and nearly indistinguishable.

Sometimes you want to talk to people without giving them your phone number. Imagine IRC but much more convenient.

How do you do groups texts?