Appliqué isn't something you see a lot of in yarn-related crafts. It's more common in crochet, but very difficult to track down in knitting, despite the interesting effects you can achieve.
Why is this? My theory is the sewing. It's an interesting thing about knitters and sewing - even if they happen to be "sewists" as well, it seems as though most yarn-artists would rather the act of sewing never come near their projects. Consider the popularity of seamless projects. The knitting will stay on this side of the fibre fence, the sewing will stay on that side, and never the twain shall meet if at all possible.
Well, I am here to make a case for this Romeo-and-Juliet pairing, and the case is appliqué.
The main reason for my appliqué advocacy is this: it is a fantastic way to familiarize yourself with shaping and three-dimensional techniques on a small scale. Essentially it's like swatching, but when you finish the swatch it has a purpose and a destination other than filling out the back of your swatch drawer/basket/box or protecting your table from your tea mug. Appliqué might just be the answer if you are among the many who think of swatching as a waste of time... (tsk, tsk, tsk).
Particularly if you're a new knitter or crocheter, appliqué can be a way to up your game - it might be still the minor leagues in terms of techniques, but it's a great stepping stone to the majors.
I encourage you to explore the patterns and ideas I've assembled on the Yarn Club Pinterest Board and see what inspires you.