A prioritized plan for the next 12 to 24 months, so upgrades happen on your schedule instead of the day something dies.
Waiting until something breaks to replace it means upgrades always happen at the worst possible time, usually mid-crisis and over budget.
A roadmap lays out what needs replacing over the next 12 to 24 months, in order of actual urgency, so you can plan the spending instead of reacting to it.