First of all, I've only been using Solidworks 2018 for about a year. Previously, I worked in CATIA V5 and have over 10 years experience in that.
In my example, let say I have two parts in an assy. Both parts are floating. If I create a mate between the two parts, which part moves and which part remains stationary? In CATIA, the first part you click will always be the part that moves, assuming there are no other constraints on the parts.
Actually, while typing this, a coworker informed me that Solidworks make that decision based on which part is first in the tree. The first of the two parts in the tree will always be stationary.
Knowing all this, is there an option in Solidworks to alter they way this behaves? To me, it make sense that the first part a pick is the part I want to move. It would be nice to have Solidworks work that way.