task manager - What is Windows Priority and Affinity and what advatanges does it provide?

What exactly is Priority and Affinity (found within Task Manager) and what are they used for:

In what situations should/could they be used and what advantages are found while customizing these setting.

Answer

Setting affinity does do something, but you'll never want to use it.

Setting the CPU affinity forces Windows to only use the CPU (or cores) selected. If you set the affinity to a single CPU, Windows will only run that application on that CPU, never on any others.

Windows automatically puts run applications on the least-busy processor, so limiting it to a single CPU doesn't let Windows do its job. Even if CPU/core 1 is busy running other applications, Windows won't be able to run an application with affinity set on CPU/Core 2.

Really the only reason you would want to do that is to run an old application that doesn't work correctly when running on a multi-CPU/Core system.