For example, say one needed a device that stops time. It doesn't matter to the plot what the device is; just that it stops time. There's no misdirection; the reader is meant to know as soon as it shows up what it does. It's not meant to have any cool value; it just needs to perform this one specific plot-related function.
If one just caves to cliche and makes it a pocket watch, already, think of all the paper one could save. (bad guy pulls watch out of pocket; clicks stem; time stops. no explanation needed. yay! trees saved!)
...of course, 95% of the time, after one presents this clever justification to one's self, one will realize that one was, in fact, just justifying laziness.
But the other 5% of the time, it works really well. ;-)