Phased vs Big Bang Implementation Approach

We initially planned a “big-bang” go-live for our HCM, ERP, SCM, EPM, and PAY implementations. However, due to project delays and an upcoming hiring surge, we're considering a phased approach for HCM to go first to accommodate the hiring surge.

 We're interested if others have done the same and could share the pros and cons of a phased rollout, starting with HCM and followed by the rest of the modules, including Payroll (in the legacy system, Payroll is a Financials module and totally independent of HCM). We'd like to learn from others' experiences with similar phased rollouts, particularly regarding potential challenges and benefits.