I'm not sure what you mean by "standard DB queue" (perhaps you mean a message queue, I guess?), but yeah Redis (or really, Valkey, now, since Redis tried to change license on everyone) is a very important tool in the toolbox for system design. In-memory databases trade persistence guarantees for raw throughput, and are very well-suited for different workloads than a traditional database is. It's great for caching, rate-limiting, realtime analytics, leaderboards... Basically anything with ephemeral data or data that can easily be reconstructed from some other source of truth. It's an optimization tool that can significantly reduce the load on your primary application database for certain workloads (and achieve higher throughput).