What is ssh-agent's role in Mint's X login?

[Kudalufi]

I am having some issues around ssh and I would like to know exactly what ssh-agent's role is in Mint's login process. What is its intended purpose, can it be disabled and if can be then what are the ramifications of doing so?

tl;dr My password stops working for an ssh key some minutes or hours after it is first used until/unless ssh-agent is killed and restarted.

Explanation follows:

I have until recently never bothered with passwords on my ssh keys, trusting to my system security. I now need higher security for one key and so I created it with a strong passphrase. Generating and using the key the first time worked as expected. An hour or so later I attempted to use the key again and the password ceased to work. The password was generated by and stored in keypass, and believing I had used the wrong entry or made a mistake in keypass, I went through the process again. I generated a new ssh key, stored it the public part on the remote server, and connected. Again, I was asked for the password and was able to log in. I did this a few more times, ensured everything was functioning as expected, then did other things. A couple hours later I went to use the key and was again told the password was wrong. I could not log into my remote system, I could not even change the password on it locally. The password would not be accepted in any circumstance. When the ssh key you just created with a password generated from and stored in keepass stops working with that password after an hour, you start wondering some real tinfoil hat scenarios. In the end I tracked it down to ssh-agent. Restarting ssh-agent corrected the issue temporarily.

I have read up on ssh-agent but I cannot fathom its actual purpose in Mint's X login chain. Ssh-agent is supposed to be an ssh key password cache, but in Mint it does not appear to actually do that. I can create test keys with passwords and they never appear to be cached. Every time I use or reuse any password protected ssh key the system asks for the password.