What is the purpose of 64-bit? I'm not suggesting we do away with it -- it has 80+ followers and over 2,000 questions -- but I'm genuinely unsure of when it should be used.

I see it (and 32-bit) used sometimes to specify which version of an OS is being used, sometimes with respect to a processor, and sometimes when the distinction is causing an issue with installing or using a piece of software. I can tell in a lot of cases that the tag is irrelevant to the question.

So, when exactly should 64-bit be used?

I'd like to get some community consensus and then edit the tag wiki excerpt to include some sorely needed usage guidance.

Then, cleanup?