title says it all, why do a PC or NVR. Cost, options, reliability?

What are the reasons?

With an NVR you get everything you need all ready to go in a factory configured box.  Just add a hard drive if it doesn't come with one, connect your cameras, and you're up and running.  The downside is that you may be limited to cameras from that one manufacturer, you're limited to a small number of cameras, you're stuck with their embedded software, etc, etc.  Easier to get running but you're stuck with it the way it came forever.

If you use a PC you get to choose the hardware and the video management software running on it.  You can do anything with it and expand it to any size or capability you want.

Do you want a plug and play appliance or do you want to be the system administrator with full control?