The function of informal rules is to keep the organisation responsive, even where formality would be overburdened. Informal rules apply. when behaviour is expected from members of an organisation, even when this is not written down anywhere and it is regarded as a condition of membership.
Organisational dynamics regulate the unwritten, non-verbal communication or the uncommunicable (all aspects of the informal), so that they can cope with contradictory situations. Formal rules are too definite, not sufficiently ambiguity-competent, and, when relied upon alone, too inflexible to react to dilemmas. Here, too, the world’s ambiguity and turmoil come into play. Scope for manoeuvre comes about through informal possibilities. You can violate official rules with a ‘good conscience’, because “Here one is simply allowed to do this” (or even must do this)!
You can find informal rules in open and latent forms. Unfortunately, these are often lumped together.
Everyone is familiar with open, informal rules and can give information about them when questioned (“At our place it’s ok to arrive 15 minutes late.” or “Here we say hello with a handshake.”). In the case of latent rules, it is different, i.e. “Nobody contradicts the owner, because he always takes revenge!”. If such a thing were openly expressed, it would be too shameful, too destabilising or too dangerous. The rule can only fulfil its function as long as talking about it is taboo. It is, therefore, naïve to believe that one always does something good for a system when the latent is uncovered by outsiders (such as consultants).