My friend and coach Tony Blauer said, "In a real fight, experience is something you get shortly after you need it."
The goal of training should be to safely replicate what happens in real confrontations or portions of what happens in real confrontations. There are several ways to do this.
You can role play and practice diffusing altercations and setting up protective tactics.
You can practice many repetitions of responses to aggression/ attacks, escapes and improvisations against cooperative and progressively resisting training partners.
You can gear up and beat on one another full blast.
I personally think that there should be a balance between these three to gain optimum benefit for Self Defense training. How you divide it up is a personal preference.