They were being used for CPU cooling by enthusiasts in the early 2000s, in combination with water cooling. Having a peltier device in it adds so much heat to the overall system that it's really only a measure of last resort in terms of bulk heat transfer.
You also have to be careful that the cold side doesn't get so cold that water condenses around it and into the CPU socket. That was an expensive mistake.
TEC's are pretty cheap and can be had for around $2 for a 100 watts of cooling power unit (plenty for a typical refrigerator).
The thing that stops their widespread use is their very low efficiency. You need big noisy fans to get rid of all the waste heat from the hot side, and that drives up weight, price, size, etc. In nearly every application, gas based refrigeration systems win out overall.
TECs have a very low delta-T limit, rapidly lose efficiency, and those internal losses quickly constrain multistage systems that try to workaround the limits.
Many consider them a niche part with narrow applications. =)
Of all the power you pump into one of those modules get 5% cooling and 95% heating. It's practically like running resistive heating.
They're not so much useful for cooling as they are for achieving sub-ambient temperatures where power use isn't a problem. Extremely light and compact fridges/freezers. Final stages of quantum computers to really get down to that zero kelvin.
