Direct change over is the simplest option but a very dangerous one. New systems, classically, will have problems with them. This could be bugs, lack of training or lack of understanding of the new system. So just swapping the system straight away could mean a loss in productivity or worse if the new system completely fails. Even though the system will have been tested this is no guarantee that it is working.

Direct change over is best when there is no system that currently exists. For example installing new a new traffic light system on a road that has never had them before. In this case, even if there are some problems, it would be better than having no system at all. Direct change over should only be used if there is no old system or the old system is broke or unworkable.