There's one website I run where we were getting some spam through the "contact us" form. No problem, I'll just install captcha. I looked at the docs and realize

There's one website I run where we were getting some spam through the "contact us" form. No problem, I'll just install captcha. I looked at the docs and realized it was more effort than I was willing to spend to kill a few spam messages a week. So, I just added an extra input field where the user has to type in "123". No spam since. I thought it was kind of funny how easy it was to defeat the spammers, but on the other hand, there are so many easy targets that it's not worth their effort to try to overcome something so elementary just for our site. Conversely, there are much higher value targets where captcha is very valuable and worth the effort to implement because it is worth it for the abusers to try to defeat them.