If you are building a new system to support a process that has not had IT support earlier, you can build it in one large chunk or in several smaller chunks. The advantage of the large chunk is that you only have to spend resources on one go-live process. On the other hand, if something does not work, you might have developed hundreds of screens with a wrong approach and have to change them.

If you are replacing an existing system (for example, an Oracle Forms-based system), you need to decide if you want to attempt a "big bang" replacement of the entire old system with a new one or if you want a phased approach. As it is much easier to run one system than to run two, some people prefer the "big bang...