Wasn't AFP deprecated in Mavericks? I'm fairly certain that it hasn't had an update for some time. At this stage, it's certainly advisable not using it for critical applications.
It probably is (and e.g. you can't do AFP shares of APFS drives), but Apple's SMB implementation is fairly bad, and sometimes the only workaround is to connect via AFP instead (sometimes I've also had much better performance over AFP)
