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.

In any real system, though, you will eventually need something to handle a certain set of tasks that are common to most busy web sites:

• Static/dynamic content caching
• URL rewriting (for many reasons)
• Load balancing among many backends
• "Sorry, we´re down" style maintenance pages
• Request blocking for various reasons
• Internal redirects