Why do so many developers apply for outline planning permission rather than full planning permission?

A possible reason is given in a comment on a blog quoted below which is about a shortage of planning officers due to cuts:

“The reason for the gap is developers have found a gap. They go for outline planning permission with the minimum of detail hoping the details will be left to reserved matters, and with planning departments under pressure to provide housing, the developer hopes he can push the development through with the minimum of restrictions Laurie Pocock”