[nradov]

A little friendly competition is a great motivator in sports that can be easily quantified like running, swimming, bicycling, and weight lifting. For me it really helps in staying fit. When you see your friends posting their workout times and speeds on social media it gives some positive peer pressure to get off the couch. Most of us here have sedentary jobs that are literally killing us so we need to get moving for more than just enjoyment.

Of course, everything in moderation.

[InclinedPlane]

I would modify your word "friendly" to instead be "playful". Competition can be healthy, beneficial, and fun, but usually only when it's playful. Consider the difference between a couple kids playing baseball for their own amusement on the one hand and a bunch of stressed out, angry, yelling parents at a little league game. There are extremes to competition and often the point where you try to win at all costs is where things break down and the negatives have the potential to overwhelm the positives.