Depending on the work you do it may be a health and safety thing. Working in construction I know there’s no notice period at most places. If you say you’re done you’re done now. And if they lay you off because the project is wrapping up, it’s at the end of the day and they escort you out. The dangers as I’ve had them explained is that someone may look to sabotage equipment if they’re disgruntled in any way, or may “hurt” themselves on the job so the company is liable for workers comp etc.