It's hard not to have some sort of review process if you want to be able to fire someone. If anyone challenges their dismissal for performance reasons, you'll want a record of the "conversations" (1) you had. This is why a lot of review processes include some sort of sign-off by the parties involved.

(1) Scare quotes around "conversations" because I've never seen management approach an underperforming employee and then realize that they had a big part in that. Conversations tend to be more two-way than that.