While re-organizing my stash of threads last week, I got to thinking about the various types of variegated threads I consider crucial to have on hand.
My first choice to always have on hand is green variegated threads, because they are sooooo handy for creating complex and dappled greenery, such as bushes, trees, grass, and leaves.

Monochromatic or more mixed in colors, greens are invaluable for creating the illusion of depth in a canvas. It's really a very simple "shortcut" to creating a sophisticated look in your project. Here's a variegated tree from one of my house designs, to show you what I mean:

Another necessary variegated thread color is brown - or rather all sorts of browns and greys and rusts. Why change thread colors for individual bricks in a walkway or chimney when you can let the variegated thread do the color changing for you?
(Hey, save your concentration for those really challenging projects, and let the thread do the color-changing work when you are stitching lots of tedious bricks or stones or shingles.)
Here's a walkway done with variegated browns and greys just like stones:

Oooooohhhh, and here's another MUST HAVE color: yellow!

You know...for all those glowing windows inside your houses... whether you use bright yellows or softer oranges, they really add a cheerful and cozy look to a stitched house. Don't you agree?

And how about all those Santas you stitch every year? Have you tried a variegated red for your santa's coat? And there are soooo many different reds - bright, dark, victorian, dull - it all depends on the look and feel you want your santa to convey...

And then there are variegated oranges you'll need for all those pumpkins you stitch.... and purples for witches cloaks.... and pinks for little girls' dresses..... blues for skies..... whites for santas beards.... You see how variegated threads can change your stitching life?!
So, next time you're in your Local Stitchery Store, take a look at all the variegated thread, and maybe grab a skein or two or three or more just to have in your stash....
(Trust me, you'll find a use for them sometime, somehow, somewhere -- I promise...)