At my previous job (industry-specific CMS supporting many websites) we used redis simply as a distributed cache to support our this application since it was deployed to a load-balanced webfarm. The CMS platform we were building off of had its own webfarm-cache solution but we found it to result in a lot of inter-server communication which only hurt our load issues even more. Redis came in as a very simple out-of-the-box solution to that problem and performance was improved tremendously. I abstracted the client in case we had to switch to Memcached etc but Redis really just knocked our socks off and the documentation was a godsend. I left before adding Redis Cluster to our stack unfortunately but I did get to experiment with that and it also looked very promising. Having used it I strongly recommend my colleagues look into it anytime caching comes up.