Dummy question but what is the purpose of grouping objects and when should it be done (before or after the tool paths have been established for each object)
I group when designing when it’s convenient to move things as a unit, or if I need to preserve a complex selection for making Toolpaths.
As Will says, definately group objects that will share a common toolpath. But, unless it’s been changed in lagter versions of CC, be sure to select the group in the Design window; if you attempt to do so in the Toolpath window, only a single object will select.
Unfortunately, that behavior has changed in recent versions and grouping is now respected in the Toolpath pane (I found the old behavior useful for selecting individual elements without the need to go back to the Design pane and ungroup).