Hey,
I'm not sure if there's not already some way to do this with playMaker, but this action lets you get the bounds of an object. To understand what bounds are, add a box collider to any gameObject in your scene. Those are the dimensions of the local bounding box, also call the rendered bounds.
So if your actual mesh changes ingame (like if you're using a text system like toolkit2D or the like) you can call this action and then set the collider size to the vector3 value this action returns.
So the global bounds is like the local bounds, only that it does not rotate. It will calculate itself from the most right/left up/down forwards/backwards points of your mesh and it will always do so while being aligned to the axis.
More visual, if you have one rotated box in the scene, then the global bounding box will give you the size an unrotated box needs to completely surrond the rotated box.
All in all this can be used for all kinds of things, including manual collisions and the like.
Cheers,
Sven