Not only a lack of rostering agreement, but in most countries still a mental leave system, month off in winter, and 10 ad hoc days for the rest of year. If you you have kids you can basically kiss goodbye any form of leave with your family in the summer.
At j2 (could be mistaken, please correct me) do they not get 36 days leave vs ryr 28 (18 days assigned in ryr month off even if that month you was only rostered for 15 days..) and 36 confirmed bookable days off? A much better system, far better than the 5/4. Most people again this year will be assigned pretty much all their leave in Jan-March, leaving potentially 11 months without leave...or worse, leave in January, and not again until December the following year, nearly 2 years without any meaningful leave, and this does regularly happen to many crews.
And do not forget, the 5/4 is there for Voldemort’s benefit, not yours, never believe otherwise.