Off-the-shelf software wins when your business process is fairly standard — accounting, basic HR, generic project management. These problems have been solved thousands of times, and ready-made tools benefit from years of refinement you'd never be able to replicate cost-effectively on your own.
Custom software earns its cost when your process is genuinely specific to your business — a workflow that doesn't map cleanly onto any existing product, or a combination of requirements that would mean paying for three or four different tools and stitching them together with manual work in between. In those cases, the "cheap" off-the-shelf option quietly becomes expensive: staff time spent working around the tool's limitations, data re-entered across systems that don't talk to each other, and workarounds that eventually break.
A middle path exists too, and it's often the right one: extending or integrating existing software rather than replacing it entirely. A CRM connected to your accounting system via API, or a custom reporting layer built on top of an off-the-shelf POS system, can deliver most of the benefit of a custom build at a fraction of the cost and risk.
The decision ultimately comes down to a simple question: is this process a genuine source of competitive difference for your business, or is it a solved problem you're better off buying rather than building? Businesses that answer this honestly, project by project, tend to spend their software budget far more effectively than those with a blanket policy either way.