Buildings are always done in grand design mode. You cannot change the building once it is built. Simple echanical devices, on the other hand, are often done using the evolutionary method--the core functionality is completed first and then more functionality is added later. The most sophisticated devices, though, tend to use grand design. This trend seems to be echoed in software: easy programs are built in an evolutionary way, but complex interlocking systems are designed and implemented in one step.

There is no question that doing everything at once has advantage of speed, but the hazard is that if the design is flawed the program has to be gutted and re-written. Evolutionary programs have the defect that their parts are often inconsistent with one another and they tend to have a lot of redundant code. The advantage of evolutionary programs is that you have a demonstrable result sooner and you have a working program to fall back on if the more complex parts of the program turn out to be impossible.

Personally I tend to prefer the grand design approach in most cases. In the long run it is usually more beneficial to have a program that hangs together well and has a unified shape to it. Projects done piecemeal have a way of never working quite right because the parts were not made together. Making a grand design is only advisable, however, when the architect has experience with the planned mechanisms. The evolutionary method recommends itself when something new is attempted because it is often not until a (semi-)working program is achieved that the toughest problems become apparent.