Answers to this would be all over the map, but I'm going with "no."

If I/we make a job offer to someone, it's because we think you're a good fit and you will be productive. Bringing someone in for 2 weeks, then someone else in for a month, then another guy for 2 months wastes even more time than just interviewing them each for half a day. Not to mention the uncertainty and morale effects on the rest of the team.

You might be right. I think you're underestimating the psychology of the contract idea, but hey, what do I know. :)

At least in California, you can be fired at any time for any reason. You are essentially on contract whether you know it or not. So whether it's 3 month or 1 year, it really doesn't matter. What matters is if you want to have the job, and if you're qualified for it.

I think it's better if there's a new hire that isn't working out, to just give them some severance pay and fire them quickly. Obviously you should be hiring with good intentions and believe that they will do well after due diligence, so 50/50 isn't a good probability to hire someone, it just causes a lot of disruption and lot of bad will.

Virtually every state in the country is at-will, which is a good thing. But the norms of this industry put the onus on the employer to (a) verify that candidates can execute before extending offers to them and (b) demonstrate conclusively that the fault is with the employee before terminating.

A trial period essentially tells candidates "your first three months on this job are a kind of extended interview". People are rejected after interviews based on standards of evidence far, far lower than the ones commonly used to terminate employees.

I'm fine with employers hiring in good faith, and then firing within a few months if the candidate isn't a good fit. It's far more efficient and easier for everyone that way, instead of dragging down the team, creating a burden on others, etc.

Why? If it's at-will, they can fire him at any time regardless.