[piaste]

Your application and runtime are probably tuned to act as servers, with short-lived requests and little or no persistent stage, and they may not play well with keeping a bunch of persistent data around forever.

I personally first reached for Redis when I needed to asynchronously process a bunch of JSON uploaded by clients via POST. I initially just stuck them in a ConcurrentQueue in memory, but no matter how much I fiddled with HostedServices and BackgroundWorkers and whatever the MS documentation recommended, the ASP.NET Core app would occasionally 'lose' that queue before it could be consumed (or the consuming loop would get stuck, with the same result).

You are also probably running your app on a pretty high-level language, with bytecode and reflection and all that nice stuff - if not even an interpreted language - while Redis is raw C code and will outperform your homebrew double-linked list or hash set.