What is custom software, and when is it worth it?
Custom software is built for one organisation's workflow instead of a general market. It is worth it when the process is a competitive advantage, when licensing costs exceed ownership costs, or when compliance requires data to stay inside your boundary.
It is not worth it when a configured SaaS product covers 80% of the need — the remaining 20% rarely justifies the build and maintenance obligation you take on.
A useful middle path is an integration layer: keep the SaaS tools, and build the thin custom piece that makes them behave like one system.