What is missing in Creo is the intuitive option of selecting a Plane of Symmetry within the Pattern command. I don't want a mirrored copy of my component(s) in an assembly. I want a linear pattern about a plane of symmetry. Of course, after some digging, I discovered that you use the unintuitive Create Component command. (I want to pattern an existing component, not create a new one...) Then you give the 'new' component a name which is a completely useless step when you want to mirror the placement of the existing component rather than actually create a new mirror image part. No new file is created with that name that I can tell. I use names like "useless", "asinine", and "stupid" just for spite! ;-)
Then the key is to select the 'Mirror placement only' option. The rest of the procedure is intuitive.
In the Pattern command, you can use the Direction option and select a plane, but the distance you enter will not update if you modify the placement of the original component. You pattern using a plane as a reference, but it is not a plane of symmetry.
You may encounter a similar situation using the Repeat command. You can select a distance constraint referenced to a plane for the repeated component. But again, that distance is not linked to the original component, so you don't get the desired plane of symmetry for your new instance of the component.
Enhancement request: Add a plane of symmetry option to the Pattern command.