If every device in the house already lives in one brand's app, a hub often solves a problem you don't have yet. The moment that changes is when a second brand enters the picture — a lock from one company, a thermostat from another, a light strip from a third — and none of them agree on how to talk to each other.
A hub's job is translation, not magic. It takes the "turn off" signal from one ecosystem's app and turns it into something a completely different device understands, so a single routine can reach across brands instead of stopping at the edge of one app.
Matter-certified hubs make this easier than it used to be, since Matter standardizes the handshake between an app and a device. Thread adds a low-power mesh network underneath, so battery-powered sensors don't need to constantly ping a Wi-Fi router to stay responsive.
The trade-off is one more piece of hardware to maintain, and one more thing that can go out of date. Before adding a hub, it's worth listing every device already in the house and checking how many actually need to talk across brands today — versus how many are already coordinated well enough inside a single app.
A reasonable middle ground: start hub-less with a single-brand ecosystem, and only add a hub once a second brand's device is genuinely needed for something the first one doesn't do.