The short of it is that one of these is an HTTP load balancer that does caching and the other is a simple key-value store. You should pick whichever one is appropriate for your particular needs.
Most of the time I have heard of people using memcached to store rendered content, it´s because they already have a robust load balancing system and don't want to deploy something else, or it´s because they need something to serve as a Source of Truth in their infrastructure -- something that memcached can really help with.
I.e., if you already have a working system, it is probably a far easier path to spin up a memcached server and then write a little code to check it before you spend the CPU cycles to build the output again. This is a very quick way to get some extra performance out of your infrastructure and it doesn´t require any real changes to the way your system works.
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