Figure out which Agile approach better suits your needs: flow-based (Kanban style) or timeboxed like Scrum and SAFe.
There are two distinct coordination issues to address in a scaled organization: What approach will the organization use to plan work across multiple teams, and how will it time the integration and delivery of software across multiple teams? The solutions to the two problems are not necessarily the same. In fact, it's usually best to use a mixed approach—a timeboxed or hybrid approach to plan large features at the front end, and a flow-based approach at the back end to continuously implement, integrate, and deliver improvements to the customer.
Which approach should you use at the front end?
As a general guideline, feature teams benefit most from a mixed planning approach at the front end, using flow-based (Kanban-style) planning for customer-driven features and quarterly (timeboxed) planning for large, strategic initiatives.
The flow-based portion of the budget enables teams to respond quickly to learning, rather than waiting a quarter or more to apply newly gained knowledge. This part should be set aside for small efforts that can be handled by a single team with minimal help from others.
However, many organizations with which I work have discovered that when they rely solely on flow-based planning, the product becomes fractured because the approach encourages teams to think locally about their aspect of the product instead of having a whole-product orientation. Moreover, they're finding that an overdependence on flow-based planning makes it difficult to get big, product-wide changes off the ground: with each team working according to its own timetable, it's rare for all teams required for a large initiative to be free at the same time. Also, because there is no designated time when all teams meet to consider the next planning cycle, there is no obvious opportunity for stakeholders to gather and make their case for major initiatives so that they can be compared and prioritized.
Why you should reserve some of the budget for timeboxing
To avoid these problems, an organization should reserve some of its teams' budgets for pre-planned, timeboxed work—large product-wide work items that teams commit to before each quarter. The timeboxed portion of the budget ensures that there will a designated time—the quarterly planning meeting—when all teams will be free for product-wide initiatives, and stakeholders can lobby for large work items.