Lego is such a great thing because it is made of simple components. When you build something out of it you can take it apart and build something different out of it. It is fun. If a piece breaks you can take the model apart, replace the broken piece and reassemble the whole thing. Great.

Of course this modularity comes at a price. Building the model of a fighter jet from Lego is much more difficult then building it from a plastic construction kit. Also the result of any Lego based attempt will look a little 'bricky'. On the other hand, try to build a ship out of your fighter jet construction kit.

So there are benefits to modularity and there are benefits to sacrificing this modularity.

This is pretty obvious, isn't it?

Yet in software development modularity is required almost every time, without considering the cost of modularity.

Also in software development modularity is sacrificed to budget and time pressure immediately, often before testing and documentation, also without considering modularity.