Why do official Lego sets sometimes use 1 large part when several would work just as well? One of the things that makes Lego so great is the ability to rebuild sets into something new and different. However, I know that sometimes TLG uses large pieces to lower costs and/or build complexity. Some examples:


54092cx1 - Plane nose
30295 - Large car base
6082 - BURP


It seems to me that some part choices are quite strange. For example, 7346 - Seaside House contains 2 1x2x2 bricks and 28 regular 1x2 bricks in medium blue. It doesn't seem like the double height bricks provide a much simpler or sturdier build, and the part is less reusable. I would have rather seen 1x2 bricks used throughout, especially since this is a Creator set, which focuses on being rebuildable.

I also found it strange that they chose to use 1x2x2 bricks in two places, but kept 1x1 bricks stacked 5+ high in others. It seems that if the goal is to create a sturdier model, replacing these stacks with 1x1x5 bricks would have been a good place to start.

So, I guess my question is: what goes into the decision of which specific parts to use in a production Lego model?
Some of the reasons (including some you've mentioned):


To make building easier / sturdier, so that the set is more suitable for its intended age range
The larger pieces are sometimes cheaper than the component pieces would be
The component parts may not be part of the current inventory of parts available to designers
To make the build interesting
To provide an interesting variety of parts


In the case of the set you mention (and this is pure speculation) it is possible that 1x1x5 bricks are more expensive to make or that they were unavailable in the right colour at the time the set was designed. At the same time, the designers might have felt that the 1x2x2 bricks reduced the part count to the extent that the set was viable for the intended market.