In my assemblies, I use rectangular patterns A LOT. When I first started, I would click on an edge of part in order to select the axis I wanted the pattern to follow. The problem with this method is that if I edited the assembly I might replace or remove the part I used create the pattern. If the part I used changes, the pattern fails.
Now I move to the top of the assembly browser, then chose the axis I need. The problem with this method is that I spend a lot of time moving around the browser.
When choosing the axis I need for a pattern, it would be nice if I could click on the appropriate axis on the USC icon. This would save quite a lot of time.