The alternate greens tend be used on Mondays during the summer, when there are outings. So, whenever big groups pay big money to play the course, they usually don't get to play three of the more outstanding holes (6,10, and 16, as mentioned), and none of the "temp" greens have even remotely equal playing characteristics as the original(s).
There was also an alternate green constructed to front right on #14 when there was discussion of renovations to the green itself a number of years ago. The work to the main green is yet to be done (if it ever will be) but, just in case, they still maintain the alternate, which, interestingly, has the purest stand of bent grass on the entire golf course.