Within the Time Off Types Edit page there is a "continue to accrue whilst booked" field, If set to YES this will ensure this holiday allowance will continue to accrue even if some of the time off allowance has been booked to be taken. If set to NO then during an instance of this time off the employee will not accrue any leave, this can cause some confusing discrepancies when checking employee time off allowances if it is incorrectly set, if set to NO mistakenly the employee's time off will be below the expected value and vice versa.