If you like prototyping projects on breadboard you probably know how frustrating is to do same initial wiring of microcontroller part is. We always have to take care of power supply caps, crystal, reset circuitry and ISP header. So why not to build this part once and then focus on further more interesting tasks.
So breadboard header for ATTiny 25/45/85 is meant to make easier with this routine task. It is assembled on a small PCB that has pins compatible with breadboard holes. Besides mentioned above it also has power LED indicator and even additional PORTB pins where you can plug any interface instead mounting to breadboard. It also has convenient socket for resonator in case you will need to use different frequencies. I’d say this is a fully working development board with breadboard capability.