"Why is running the autostart mode actually so bad?"
Because there's code that runs OnLoad or OnOpen of the autostart form, this code does a bunch of stuff we do not want to run.
As I stated, point is to develop an "Object Dependencies" like the current Access attempt but from A.accdb that confidently says
"this object found in B.mdb is never used anywhere in B, neither in its SQL, VBA, never referenced in Forms or Reports, neither in any subform or subreport."
As a result, we can systematically clean-up these old MDB files that contain a lot of garbage objects that no one ever dared to delete e.g., query1_old, zzzzQuery2, Form1_old, etc.