Usually when I’m just looking to have some fun and don’t really feel like laddering or bothering with any human nonsense, I’ll crank up the ol’ AI and start practicing away at Protoss or Zerg, my two offraces. I do this for two reasons. The main reason is that, well, I’m still just a Bronze level player and by the time I get higher in the ranks, I may want to focus on a different race, so each deserves their fare shake.
Two, it helps me get a better understanding of what my opposite-race opponents are going to do on the ladder. While by Z or P is not nearly as good as my T (and my T isn’t that good to begin with), it isn’t exactly the most scientific of tests, but it has helped in just preparing me for certain timings and certain builds in a much more entertaining way than watching a video on YouTube or reading a forum post.