There is a well-known and long-standing problem with initialization of the plug-in that can cause SketchUp memory usage to run out of control until your Mac crashes. A (admittedly awkward) workaround that works for me is to immediately close the default blank model window the instant SketchUp starts. If you are quick enough the memory leak won’t happen.
Despite multiple complaints from many people dating back at least several years, 3dconnection lacks either the interest or perhaps the competence to do anything about this bug.