My mom used it quite often in middle school when I graduated from clear mascara and lip gloss to some more experimental make up decisions. Think blue eye shadow, bubble gum pink blush... You get the idea.
The saying originates from Shakespear's King Lear and has since been in our vernacular as an appropriate descriptive phrase for unnecessary ornamentation. In other words, why would you guild the lily when it is already beautiful as it is.
While I LOVE LOVE LOVE Tridacna Gigas, better known as Giant Clam shells, just as they are:
(Sidebar: I'm lobbying for a sink like this in the new house's powder room....)
...I can't help but think that in the case of our Giant Clam shell from Regina Andrew, a little gilding is not unnecessary at all: