A Git SSH key represents/identifies what?

Context
With Anvil’s Git integration, I can clone any of my projects to my local hard disk, and re-create Anvil’s project directory structure here. This is easiest if I establish an SSH key known to both ends of the conversation, i.e., to my local Git installation, and to Anvil.

Question
When there is only one developer, on one PC, with one working directory (per Git project), it’s pretty clear what this key represents. When there is more than one, however, is there any advantage to using more than one SSH key? If so, what meaning would you assign to each additional key?

It’s common to have different SSH keys on different machines - eg I have a separate SSH key for my laptop vs my desktop vs my phone. I’ve added all three to my Anvil account so I can push/pull my apps from different places.

There is a per-computer, per-user key folder, in Windows, which suggests that a key represents a specific user on a specific PC. But there are so many alternate conventions that could be applied in practice, I couldn’t be sure what the practice actually was.

Thanks for clarifying.