Systems have a lifecycle. Typicaly there is a systemm development lyfecycle (provided by systems engineering) with stage-gates to mark major phases and transitions. The system is concieved, planned, developed, tested, operated and later disposed of. One system replaces another. All this takes time, and planning. Without that one system will break down as unsupporable and you may be in a huge rush to replace it with anything, perhaps not the best replacement, and you may be willing to spend extra to do it. The results of planning are reflected in the enterprise transition plan.
Investments also have a lifecycle, with reviews. These mark the ROI and the breakeven points, and should also be reflected in the transition plan.
"If you do anything long enough, you eventually get good at it." MK