I am an employer (manufacturing) in Arizona USA, a "Fire-at-will" state. If I did not have this privilege, I would not take the risk hiring job candidates who interview poorly. I would be compelled to take the obvious best choice every time, and to never take a risk. Risks are too costly.

With Fire-at-Will I can take a chance on anyone. This is especially useful with lower lever, entry positions where they learn on the job. I have tried hiring all types; the results have been surprising. The sure thing employees aren't always, and the WTF employees sometimes surprise you.

The woman in charge of my accounting, was an 18 year old goth cosplayer, moved from the warehouse to the office as helper during a layoff. She is now 22 (still goth/cosplayer) and does her job like she has 20 years experience. I would never ever have hired her for that job if I could not fire her easily. But she is great.

This is the positive side of Fire-at-will. In practice, you never fire anyone on a whim because it destabilizes the rest of the employees. I only fire the people who need it, and by then most of the staff probably wants them gone anyway.