How often do you have to warn members? How harsh are you on them? How serious does it have to be to give a warning/infraction?
It's an occasional occurrence. If the violation wasn't that egregious then they get a warning rathing than an infraction. If a member continues then the punishment will increase.
I don't use an actual infraction system and just warn people occasionally if they get out of hand. Most times, I don't even have to do that, though, and it's usually only in connection with someone getting slightly spammy or breaking a rule they might not know about.
I used such a system on a forum of mine, until I got the community in line with our rules. Now I don't need to do it anymore, I just send a PM if needed. For the serious stuff (spam or trolling) I instantly ban, for the rest I just PM the member and solve the problem.