Long ago, we started using the issue tracker JIRA to support our development projects. The main reason we chose JIRA then was the awesome custom workflows.
We had specific requirements for our development and support processes and with JIRA we were able to support those. It was also super easy to connect clients to their own support project and to give them a live view of the development status of their products.
Nowadays, aside from development, we use a bunch of different types of workflows, for example: for invoicing, recruiting, first-line support, second-line support, lead management, maintenance and many more... This helps us keep track of everything that's happening in our company. These workflows allow us to continuously measure and improve on our efficiency.