I had some fun with my 7 Reasons I'm Not a Runner [ARTICLE] and now I discuss the highly revered 5K. It's a popular topic, and if you go to any of the common content-mills like Active.com or RunnersWorld you'll countless articles about how to train for it, how to run it, race day preparation, in-race nutrition, drop bags, and probably even how to tie your shoes for a 5K Run. I have commented a few times that for most of us the run is less than 45 minutes and a lot of this stuff is just noise and chatter, just go have fun.
I regularly run more than 5K on a daily basis. Usually between 4 and 8 miles on trail in the mountains of Colorado. Every now and then I do less miles for more speed, but not that often. In the big scheme of things I just want to have a good workout.
Doing a 5K with any level of competitiveness, even for my own stats and PR attempts, means I bust my butt for 30 minutes, which results in having to take a week off from training in order to recover, and I came in 2nd to last in my age group.
Even busting my butt on a PR attempt results in not a lot of training effect. See how few minutes are spent in any of the training zones in the above screenshot (from a 31:25 5K PR)? From a training perspective it's not all that beneficial when weighed against the time off of training to recover from this. It would probably be far better to ride the Tempo/Threshold Zone for a 10K. Probably as well to ride the Endurance Zone for 10-12 miles.
As far as I'm concerned, for us older folks, and people who run 25 miles or more in a week, the 5K can be the "sprint/interval training day" every couple of weeks, depending on recovery issues. It can be used as training for that last kick at the end of a longer run. I might do one to help motivate and inspire a friend or relative, a young runner, and give them support and pace them. Photo below is night-time trail running with my 12 year old son by headlamp.
I think the 5K is a great goal for a beginning runner. I think it's a great goal for the speed demon who can do 4-5 minute miles one after the other for 15 minutes. I think it's a great kid's run. I think a lot less stress should be put into it though for most of us who just want a great workout without getting all bent out of shape over details.