Because holiday is tracked in days and accounted for in money, in two different places. The accrual is estimated once a year, and usually wrong in the direction that flatters the result.
Attendance and leave recorded in Nest reach Books as accounting consequences: unpaid leave reducing pay, and untaken holiday carried as a liability.
Leave balances come from Nest with each person's rate. The provision for untaken holiday is calculated from the actual balance and posted as a liability, moving as balances move.
A team carries thirty untaken days into the new year. The provision reflects it at current rates, so the cost sits in the year it was earned rather than the one it is taken in.
It will not set your leave policy or choose the accrual basis. Nest holds the entitlement rules; Books records the money that follows from them.
It posts the provision to the ledger and the cost centre, feeds project cost where people are allocated, and shows on the balance sheet as an employee liability.
Yes, through the pay run in Nest, which Books then posts.
Each period, from the balances as they stand.
Yes — current rate or average earnings, whichever basis you use.
Fourteen days, every module, no card. Or half an hour with someone who will run it on your own records and tell you where it does not help.