I use crease often with subd's. Its good for me when im converting from polygon to subd often to get a smoother version of the mode.
As far as i understand it, it makes the edge sharper so as you would normally have a gentle slope between 3 angles. If you partial crease the middle angle the bend will be sharper. If you full crease it. The bend will go from the first angle to the second angle. then to the third. Almost no bend.
Test it out a few times and you should get to understand it a lot.
You could also crease a vert.