Use an existing product when the workflow is common
Established products are usually the sensible starting point for standard accounting, collaboration and operational workflows. Configuration is cheaper and faster than recreating mature capabilities.
Consider integration when information is fragmented
If the main problem is duplicate entry between capable systems, a carefully governed integration may create more value than replacing everything.
Build when the operating difference matters
Custom software becomes defensible when the organisation has a verified workflow, service model or constraint that existing products cannot support without damaging complexity.
Calculate the cost of change
Include implementation, data preparation, training, maintenance and adoption—not only licence or development cost. The decision should be based on long-term operating value and risk.
Apply the thinking