Standard functionality reduces special code, simplifies upgrades and uses patterns already tested across more organisations. Custom development preserves specificity and can remove manual work the standard does not understand. A good decision does not choose one side in advance; it evaluates business value, risk and the complete solution lifecycle.
Customisation is risky when it simply copies an old screen, avoids an uncomfortable organisational decision or supports a process that changes every month. It is equally dangerous when the request depends on one person and nobody can explain the consequence for data, reporting and other modules. In those situations, development hardens ambiguity rather than resolving it.
If price depends on contract, batch, material quality and manufacturing outcome, a standard price list may not be enough. Custom logic can be justified when the rules are stable and revenue depends on their accurate application. The calculation must still preserve input traceability, rule version and a way to verify the result. A black box that produces a price without explanation creates financial and operational risk.
After release, monitor actual usage, whether the agreed manual work falls, how many exceptions are created and whether every future change takes longer. Functionality that is rarely used but frequently blocks upgrades should be reassessed. Customisation is not permanently justified simply because it was built once.
Good custom development is not the opposite of standard. It is a bounded, explainable and maintainable extension where business value genuinely requires a difference.