A few standout highlights from MY only direct work experience involving a (1) union:
Scenario: Salespeople unionized, paid hourly plus a commission for selling widgets with an associated contract service.
Experience 1: Employee work schedule required to be posted by a manager at 9:00am Monday, was not posted by 9:15am but manager had communicated it was almost completed and would be up in 5 min, grievance filed.
Experience 2: A hungry, sales-leading newer guy appropriately requested off for a future Saturday before a more tenured rep who sold less then average and frequently caused team disruption. The tenured guy given priority for time off request.
Experience 3: Sales rep dramatically underperforming peers received verbal coaching, extra training, another coaching, then finally documented coaching: grievance filed for "being singled out". The union rep that came in to discuss the situation with manager works for a competing company. He assured manager he had no one else's interests in mind other then the employee.
Experience 4: consistent, top selling rep who is well respected comes to sales manager to ask for a raise as a competitor has approached him offering more hourly money, manager has to tell rep his hourly rate is negotiated and he cannot provide a raise outside of the standard annual review process. Rep leaves for greener pastures.
Experience 5: Rep claims he lost company-owned widget, caught using it personally, confesses when confronted, terminated. Back at work weeks later because company didn't want to fight Union in court.
Those are my experiences. I'm sure they likely don't mirror the intent of or actual practice of many unions. At least that's my hope.