When a business asks for "an ERP," the instinct is to scope the entire system upfront — inventory, finance, HR, manufacturing — and build it as one monolith. In practice, this is where most ERP projects stall.
A modular approach lets you launch with the two or three modules that solve the most painful problem today, prove the system works on real data, and add modules once the first ones are bedded in. It also means a finance module redesign two years from now does not require touching inventory or HR.