Mies van der Rohe famously said "God is in the details." This is a statement of architectural philosophy, and like all such statements is open to debate. (Personally, I prefer a good overall design and mediocre detailing to mediocre overall design and good detailing.) What I find fascinating about this statement is its context: Mies did more to popularize International-Style Modernism than any other single person in the U.S., and that style's hallmark is that it eliminated most of the details of previous styles. In other words, Mies searched for perfect details by getting rid of most of them.
An obvious example of the International Style dropping details is the non-use of moldings where interior walls and partitions meet floors and ceilings. Crown moldings and baseboards may be associated in the popular imagination with historicist architecture - Louis the 57th or some such nonsense - but they serve an important function: they hide the juncture of two planes and therefore (a) allow for differential movement without cracking and (b) allow the laborers building the walls a place for slop in measurement. It turns out that replacing the dreaded "ornament" of moldings with the "detail" of a simple joint increases the cost of construction and the amount of maintenance required. Or to pound the already-in-place nail a little harder: the building traditions of hundreds (sometimes thousands) of years had practical purposes not always obvious to those who would eliminate tradition in the name of modernism.