You can buy microcontrollers for as little as 3 cents, if you order a lot of them, a staggeringly cheap number even if you're so young you don't know a Zilog Z80 was $10 in 1978 money. But are these cheapo parts any good? Hackaday says they're terrible, but Tim finds a role.
[it] surely is a question of perspective. They address a specific category of low-cost, high volume, non-serviceable products with limited functionality. You need to wait for the push of a button and then let an LED flash exactly five times? You need to control a battery-operated night light? The sub $0.10 MCU is your friend to reduce BOM and shorten development time.
For everything else, spare a buck.