The tools you need do not always know how to talk to each other. A mobile app may need a record from an older system, or a partner may need to check availability before confirming a booking. People end up moving information by hand because the connection is missing or unreliable.
A well-designed connection gives each application a dependable way to ask for information or trigger an action. Permissions control what it can access, clear responses show what happened, and failures have a recovery path. Existing software can support new services without forcing the people using it to start over.