Apple ID: Manage Devices for "Downloads and Purchases" vs Computer Authorizations

Great products and services, but fully understanding the Apple ID, not so much.

I read support article View and remove your associated devices for purchases and see that I have 2 computers "authorized" and 3 devices "associated." What is the difference between the two and why can only computers be authorized?

One of the authorized computers does not work anymore, so I cannot login to deauthorize. I read that I cannot deauthorize just one computer, so I have to deauthorize all computers.

What does it mean if I deauthorize my current computer and are there any implications if I do? Will I be able to authorize it right away or so I have to wait 90 days?