Interesting phenomenon. Certainly not recommended for anything serious.
Most MPU's at least have plenty of different power modes which should be managed as required.
I worked in the electronics team designing Zoleo (
www.zoleo.com). The device talks to the Iridium satellite network, GPS satellites, a mobile phone, and a host of internal I/O devices. From a small single cell 3.7V battery this baby will typically operate for an impressive 200 hours between charges. One task I had was the power consumption calculations during the design, and it was not easy by any means. Every chip, pullup/pulldown resistor was analysed prior to the schematic being locked down. And within the MPU, the power consumption with different power modes under firmware control was critical to keeping current drain minimal. With most products no one cares much about a few milliamps here or there, but this application was critical because as Zoleo is used by trekkers, often in the middle of nowhere. This product is now a world beater which is a credit to all on the R & D team. A very satisfying result and a terrific product even if I say so myself.
Most small CPU's these days consume very little power and can often be left in sleep mode until an external interrupt, from, say a MEMS device springs it into action. Using PWM to reduce power consumption on a micro in this day and age for a commercial product is nonsense. Many products do not have anywhere the level of power consumption analysis done that we did for Zoleo. The importance of this of course depends largely on the application requirements.