Many big projects can be split into many smaller chunks known as components. This is a natural part of systems analysis which means that it makes sense that when the system is implemented it can be done in small chunks.

Initially only part of the new system will be used, the rest would still be based on the old system. As such, if there were some problems with the first implemented component then the rest could be delayed and the old system used until the problems were sorted.

This does mean that the old and new system must be able to work together which is not always possible. If the old and new system are completely incompatible with one another then a phased approach can not work. Phased approaches work best when it is a small company which are upgrading an existing system or implementing a brand new system, like in direct change over. It is not suitable for companies with many different premises or systems which are adding new functionality.