I use a caching plugin for similar reasons to @Devrealm_Guy, albeit that I use Memcached instead of Redis.
Most of my sites are membership sites or intranets where page caching actually harms performance rather than helping it, but using object caching significantly reduces the load on the server and allows for large numbers of people to be logged in and active on the site without impinging on performance.
Oh, and by the way, I use Litespeed Cache. It works well without a Litespeed server, but is obviously designed to work best in conjunction with one. (If you’re currently on Apache, you would see a performance boost by switching to Litespeed, and I’m told that it’s a fairly painless transition.)
EDIT:
Yes, it does have a CDN option.