Most people never see bark splitting open on a tree branch. It's usually on top, hidden like the dark side of the moon. It may or may not be a big problem. It's possible it could kill a branch, and even the whole tree in severe cases. Splitting occurs mostly on thin-barked trees, and younger ones at that.
It appears that there are a number of causes. Some we can control, others we can't. The actual cause on your tree may remain a mystery. Best thing to do is manage the tree properly.
Cracked bark generally appears lengthwise, facing the southwest. Since it's usually on top, it's open to more rot since water can soak right in, along with dust, bugs, fungus, etc. This problem can be minimized after the fact in some cases. Keeping your crack clean is probably quite helpful so that rot doesn't have much to grab onto.
The cause may be excessive vigorous growth. That's good, right? Well, it can be, but it's complicated. Like in most of life, excessive isn't so great. Growth at the wrong time of year can leave it vulnerable. So according to experts, pruning or fertilizing too late in the summer or in the fall can encourage growth that doesn't tolerate winter very well and sets up a bad crack situation..
A combination of frost and hot sun in the right combination can cause expansion of the wood, which leads to cracks. Incorrectly pruning can exacerbate this problem. It can open up too much of the canopy to sunlight, and an incorrect cut can cause a wound that opens the rest of the branch to stress. It seems best, therefore, to prune frequently and diligently rather than infrequently and heavily. That's been my motto anyway. Removing vertical water spouts/sprouts as soon as possible, at least when they're smaller than about 1/2", is a good idea. They grow faster than other branches, but weakly, and they only like it on top, so this is a bad combination. They look terrible, anyway. Most things don't look right sticking straight up.
Drought can apparently make things worse, especially if there's a sudden increase in rain. It's probably best to give your trees a drink now and then during hot summers, just to the point that it's sensible without being wasteful. You'd probably split if you didn't get a drink when you were thirsty.
You can usually tell if the branch will recover well if the bark is cleanly separated and the wood beneath looks healthy. Cutting cleanly any separated bark that allows intrusion and retention of water and yucky pests is a good idea. You'll need to read up on how to do this. If it just looks awful, it's probably gonna die sooner or later. But if there's no replacement branch in the wings, you probably should leave it for now if it's not an imminent hazard.
Check out your trees, and if they're split more often than a country music couple, read more about the subject and try to figure out what led to the problem. Fix it if you can.
You can be a TreeDawg Knight!