[singlow]

CloudFlare does more than just caching. Even on non-cached pages it can filter and otherwise mitigate traffic that it has identified as malicious.

[kalleboo]

Correct, many times I've had to fill out a captcha to load a CloudFlare-protected page.

[xxdesmus]

The sensitivity/frequency by which the captcha challenge page gets displayed is dependent on the security settings selected by the website owner.