If application of a formula results in rapid change then it won't be accepted. Quicker responses possible. Increased communication with departments. Appearance of equity. Avoids annual blood baths.
Users have greater ownership of the collection.
Most estimate budgetary needs based on industry expectations with cancellations when necessary. Prepurchasing currency at favourable exchange rates. One library has a July to July financial year which means subscription renewals are made at the beginning of the financial year. Decisions on electronic resources, interdisciplinary titles, reference titles, undergrad material - not well suited to devolving to departments. Formula will face regular challenges.