IMO, it depends on the system. The more tactical it is in character creation or in play (e.g. making a resonable, but mechanically suboptimal decision may lower the enjoyment), the more important is rule knowledge. Also, players should know the rules in games that have exotic or complicated mechanics, because otherwise play may become very slow.
In non-tactical games a brief knowledge of rules is enough. In non-tactical games with simple rolls and numbers it is possible to have a very good session with people who have never seen the rules before.
In non-tactical games a brief knowledge of rules is enough. In non-tactical games with simple rolls and numbers it is possible to have a very good session with people who have never seen the rules before.