There are different types of integration possible and there should be an understanding of what type is needed based on the business drivers and requirements. Some integrations may be required to take place in real time, where an action in one system triggers an action in an other system that must take place immediately. These types of integration can be more complex and expensive to implement.
In some cases, near real-time integration is sufficient. Near real-time integration is still quick but processing may be measured in minutes rather than seconds. If there is no requirement for such a quick action, batch integration may make the most sense. In contrast with real-time or near real-time integration, batch integration may take hours, or even days, to complete. Batch processing can be scheduled and processing can be executed during off-peak hours.
Some types of integration will be easier to implement and less disruptive to existing environments, so in addition to understanding business needs, having knowledge about the current environments is important.