I took agility classes for fun with Dena. In fact the name of the classes was Agility for Fun! I figured if she and I got good enough to compete and we were both having fun I'd consider entering a trial, but she didn't really have the drives for it.
I started flyball with Halo for fun too. Eight or nine months later we raced in our first tournament and have been hooked ever since, so you never know what will happen, lol.
I personally think that any fun activity you decide to try with your dog is a good thing, whether it leads to serious competition or not. And entering into it with that attitude - that you're trying it for fun rather than being seriously invested in having a top competing dog, is a healthy way to start. If it turns out that it's not the sport for you, or your dog doesn't seem to enjoy it that much, no harm done. And if your dog ends up being into it the way Halo was with flyball, you can always change your mind and go after it with a passion!