It would be interesting to see the data about when a company posts a job post and when it gets closed.
We can then use that data to create "trends" graph for that company.
From a candidate's perspective, this can help identify what time of the year is the best one to apply and more importantly when to start preparing for one.
• Job websites are, for some companies first and foremost, a signal to the investment community. Hey look, series A, and now we have these 12 job listings open. Meantime they're trying to figure much more important things out than who to hire at that level (like who they can get who knows how to hire). Any emails sent in go straight to nowhere.
• Quantities are going to be wrong. If you want to hire a team of 5 engineers, you could have between 1 and 20 job listings (because different skill sets might be all you can find, but that'd be good enough, or you're afraid 10 identical listings will make you look desperate).
• Job websites are out of date. A company hires everyone it needs to, it moves along smoothly, job listings are still up for jobs already filled. Why bother taking them down? Maybe you'll get an application from a rockstar who'll work for $50k and no equity at the exact instant your leader puts in his notice.
• Job listings are also a political tool. Say you have an organization with 1,000 employees and 90% of them are low-skilled H1B's. While you might ordinarily need about 50-100 job listings to keep pace with employee turnover, putting 1000 job listings out there helps give cover to politicians to expand, rather than curtail, the H1B program. Recruiting someone is expensive. Pretending to recruit someone is almost free, and unreasonably effective. Vaporware for fun and profit.
For a candidate, the best time to apply for a job is when he or she needs a job, or wants a better job. There's no Rolling Stones/Satisfaction/Losing streak when it comes to applying for work.
There's no threshold for perceived competence with most of these companies- they're happy to leave positions unfilled whether they have 1 or 1 million of them on their jobs website, because there's an endemic irrational fear of making a "bad hire" at the expense of a fear of losing good ones.
It can also tell you which jobs are potentially "fake" jobs posted for some other purpose - to signal the market, to fulfill a requirement for the H1B they want to hire, etc.