When a standard product fits
If the product matches your core workflow and the team can use it with modest configuration, a standard product may be the faster choice.
When a custom module helps
A custom module can make sense when a specific workflow repeatedly falls outside the standard product and the workaround is costly.
Check the operating cost
Compare implementation, training, support, upgrades and internal effort over time. Include the cost of maintaining custom code.
Run a small proof
Map one workflow and test it with real users before committing to a large replacement.
A practical starting point.
Every business works a little differently. Map your own workflow and check any accounting or compliance decisions with the people responsible for them.