What a custom addon actually solves
SAP Business One covers standard processes well, but almost no company operates exactly the standard way. When the team starts keeping parallel spreadsheets, copying data between screens, or repeating the same manual check on every order, there is an addon waiting to be written.
A well-designed addon lives inside the ERP: users do not switch tools, export nothing, and learn no new interface. They see one more field, a validation that warns before saving, or a button that produces in a second what used to take twenty minutes.
My rule is simple: if the standard does it, use the standard. Custom development is for what is genuinely specific to your business.