It really depends on the company you work for. I know that at many larger companies, there is all sorts of lawyer-inspired "wisdom" on how firing/layoffs and employee notices are handled. You know, layoffs happen on a Friday afternoon; immediately escort an employee giving notice out of the building so they don't bug your system, etc.
But, it does not always have to be that way.
A tiny datapoint: I work at a small company (~30 employees) in an at-will state. In nearly 10 years' employment, I have never seen an employee laid off with less than 4-6 weeks notice. Likewise, I have never in that time seen an employee leave with less than 2 weeks' notice, despite the fact that anyone legally could. The vast majority have likewise given 4-6 weeks' notice. I don't think it is coincidence :-)
I know it is not representative of all companies, but at this particular one, a security guard with a box does not materialize at your desk the moment you announce that you are leaving. There are many reasons an employee leaves; most of them are not "fuck you". In recent memory, some reasons were that an employee had to return to their hometown to care for aging parents, were going off to get their masters/PhD, or their spouse couldn't find work in the area or couldn't stand the climate, or of course the usual "better offer" / change of pace. In each case, the employee gave several weeks' notice and it was greatly appreciated. It allowed time for some knowledge transfer, cleaning up any loose ends and transitioning projects to someone else. I suspect that if the company did escort on-the-spot, or the boss/owner didn't work so hard to avoid layoffs and give ample notice when they did happen, employees would give a lot less notice too. It's really a two-way street, and depends a lot on your company culture.