On Ethereum there is no built in way to have a contract be called periodically, say every 5 blocks, or at a specific time in the future. This contract creates a market which allows contracts to hire people to call them at the requested time.
A contract is a group of functions that live in the Ethereum Blockchain (a distributed virtual machine for running decentralized applications)
> Why would people want one called periodically?
For the same reason people need cron to call periodic functions.
Contracts expose functions as an API that others can use to interact with them.
Does that mean that if 'market conditions' deteriorate or make it unfavorable to 'take the job' as it were, that the reliability of this system would take a hit?
The market aspect is more akin to a marketplace where people are hired to do a job. And the job is entirely automatable.
I'm just thinking this is really loosely tied system, and it's interesting to think of all the possibilities for how it could break down.
You are correct that it would be an interesting world if somehow demand for scheduled call execution spiked to some massive number that outpaced the ability to execute them. I am having trouble thinking of realistic scenarios where that happens but that doesn't preclude it as a possibility.