I draw cartoons regularly for several business and trade magazines. And I find that the often dry, serious subject matter usually lends itself quite well to cartoons. Whereas if someone asks you to come up with a cartoon for a story that is already funny or bizarre in some way, that's a far greater challenge.
By the way, I know there's only three legs on that chair. There were four, but it looked cluttered and distracting so I took the fourth one out! The perspective is out of whack too. But it matters not a jot, because it's a cartoon. That's the beauty of the artform. If anyone questions it you say, "Tut, That's my style..."
Over the past few weeks this has happened a couple of times with the cartoons I draw for a local newspaper group. The subjects were rotten weather (a perennial British favourite) and CCTV security cameras. The cartoons were re-drawn to fit the newspapers, but it was nice that the hard work, ie. coming up with the idea, was already done.