"The best thing in every noble dream is the dreamer." [Moncure Conway]
From employee's point of view you should plan your vacation as early as posssible. You can make sure that you will be allowed you take the intended vacation and you can make special arrangements/plans/bookings about your holiday destination.
From employer's point of view it is an operating risk to have half of the crew not taken any holiday in October, for example. Then why not asking your team to seriously plan 50% of their vacation by March and 100% by June?
My rules of thumb as a manager used to be:
1. Define which team members cannot go on vacation at the same time.
2. Ask the team to plan (everybody should plan for at least 10 days of vacation by TOD=time of delivery)
3. Single parents go first during school holidays, then parents.
4. First come, first serve after TOD.
Plan your people's vacation with:
sbHoliday.xlsx [101 KB Excel 2010 © file, open and use at your own risk, please read my disclaimer]