If you need caching in your website to make database use lower, do you have to do it using memcache or memcached (in PHP, for example) or can you achieve this by using professional services like CloudFlare, Incapsula or others like that do some caching for you?
Services like Cloudflare cache your HTML and/or assets like images and CSS files in a CDN, so that your entire server is hit less often. This is great for semi-static sites but may not be the best fit for highly dynamic sites.
Local caches like memcached just store any data in a way that's fast to access. You can use that to cache database queries and lower your database activity, but you can also use it to store pre-computed data that would be expensive to re-create all the time or whatever else you may want to store non-permanently in a fast-to-access way.
Both solutions solve different problems. You may use both together, or either, or neither. It really depends on where exactly your bottleneck is and which solution fits your problem better.