Off-the-shelf tools are fast to adopt and usually the right first step. The problem starts when the business begins to bend around the tool instead of the tool serving the business.
Signs it may be time for something custom: work moving between several tools by hand, spreadsheets acting as a system, workarounds nobody wants to touch, or a process that is genuinely unique to how you operate.
Custom software does not have to mean a big-bang rebuild. Often it starts with an internal tool, a portal or an integration that connects what you already use, then grows as requirements become clear.
The best custom systems are small at first and precise: they solve one real operational problem well, and give you a foundation to extend.