Any Union has little or no impact on the practicalities of running a successful operation
Whilst it may differ in each TOC heres a sample of how ASLEF union reps who are full time drivers have a significant impact in the running of a successful operation....
ASLEF reps were involved in the design of the cabs of Stadler 745 and 755s
That they also check every single permanent and modified diagrams to ensure they are "legal" challenging & rejecting those that are not. This alone requires a weekly release of a union rep & more during the summer and winter timetable updates.
They produce the rosters that are then agreed with management.
They produce the annual leave rosters
Work with management to specify walking times & walking routes, specifying the operational time allowed for operating trians for instance preparation times for various types of traction, the time allowed for mobilisation and immobilisation of a unit etc.
Have a separate Health & Safety rep with all kinds of additional responsibilities.
Have regular monthly meetings with management where operation requirements and issues are discussed and actioned and solved.
They may be involved with signal sightings meetings with NR
ASLEF and RMT union reps are deeply embedded in the practicalities of running a successful railway.