On one of the message boards I read, there is a discussion of knitted "food": specifically, why. Some think it's a waste of yarn, others think it could be called art and therefore be excused from function (don't get me started on this - one of the reasons I didn't do a BFA or pursue an MFA is the art vs. craft debate). Some of us think it's fun. Me, I don't just knit the stuff, I design it! So of course I had to chime in.
I don't know why, but my sushi-themed patterns have been popular (just published a nigiri sushi baby wipe cozy pattern). I'm responding to demand with this pattern, and if it does well, there will probably be more. The Knitty Gritty patterns I worked up were at the request of the producers, who saw the original sushi tp cozy pattern I did for Crochet me. That pattern also led to me writing up the all-knit version and being asked to work up the sushi pillow for the Get Hooked book (and yes, I am considering working on a knit version). The crocheted bacon and eggs handbag I did was based on a knit pattern from the 70's, and my post with the pattern has been getting numerous hits on a regular basis. I've also been working on using whimsical patterns as a way to learn and practice techniques - the Knitty Gritty patterns, for example, use short rows for the tp cozy and a slip stitch pattern for the tank runner which produces vertical stripes without having to use bobbins. Because there is something silly about the pattern, it can take some of the pressure off. Forgot to knit a wrap on one of the short rows? It's just a tp cozy! No big deal! Currently, I'm playing with ideas on how to introduce some of the techniques used for sock knitting that don't involve actually knitting socks (if it doesn't have to fit an actual foot and is silly to boot, it could be more fun than stress).
My background is in the fine arts, so I know high material value/functionally useless. I like to have at least a veneer of practicality in my work. I have, for example, numerous ceramic vessels which are currently holding everything from eating utensils to paperclips. Sure, knitted bacon could be seen as a "waste of yarn" but that could be said just as easily of an afghan knitted from luxury yarns which is only used as a decorative drape over the back of a couch rather than as an afghan because it's "too nice to use" - surely not every luxury yarn afghan is reduced to this, but it does happen. Even items which are ostensibly useful are only truly useful if they get used. By this measure, knitting a beautiful Norwegian sweater for myself could be a waste of yarn and my time, as the chances of my wearing it would be very, very low, although I might learn a lot from knitting one (which could be practical). Fancy stitch markers instead of loops of scrap yarn could be considered wasteful, or they could be considered a pleasure to look at and use, a small indulgence that makes one smile.
What is practical and useful is largely a matter of perception. If it brings someone joy to knit a hamburger, bringing a little more light and laughter into the world, I find something practical in that. If it brings more delight into the world without causing harm, it is one small step to peace. If you can't bear the thought of doing something you would find wasteful, well, you don't have to.
One of the soldiers I knit fingerless mittens for has recently returned home, and thanked me again for the mittens. They were practical - I made sure that the colors were dark (black is a favorite), and that the mittens were easy to shove into a pocket and didn't take up much space (used sock yarn at a fine gauge, done entirely in ribbing to make them stretchy). Even with the guidelines posted for those making items for the armed forces, there have been times when the items wind up going unworn by a soldier, perhaps donated to a civilian instead, because the item is too bulky, the colors are too garish, or it has a pom-pon on top of it. Does this make it a waste of yarn and time? If it tells someone far from home in a stressful situation that people at home are thinking of them and want to keep them warm, I don't think so. The moment in which the recipient knows they are loved and appreciated is plenty practical.
Besides, if you want to talk about waste, how about cut flowers that will just up and die in a week?