First of all, talking about the types of communication - two main ones can be identified - spontaneous communication and regular scheduled communication. Spontaneous communication as well as regular can be informal (most of the times) and formal.
Informal spontaneous communication is the communication that takes place every day withing the office. You say hello, you ask for a piece of paper, you ask for a signature, you talk a bit about your family, about your dog, you go for a coffee, nothing special, just regular day to day talk which occurs with no planning and no predetermined purpose. This type of communication is useful to get to know people better, to understand their likes and dislikes, their family matters. Since you spend at least 8 hours at work you need to know your manager and you as a manager need to know the employee beyond a job description. People are not machines and need to socialize and communicate in order to be able to spend productive time together.
Formal spontaneous communication occurs normally when something related to the business or to the employee's job needs to be transmitted and wasn't planned. This means that the manager communicates some new results, new tasks, something has happened and the employee needs to find out - either good or bad. This type of communication builds authority. As I mentioned it is not planned so it can also occur any time.
Informal regular communication is the type that appears during planned team buildings or evenings out. They are planned events taking place normally outside the office allowing people to learn more about each other and building a strong team. It's important to organize such type of communication for people to become a team. They are not just friends (relationship improved by spontaneous informal communication), but they are a team. It's useful during these activities to organize group tasks like games and sports matches in order for people to work together but without the constraints of the office. How often should this happen? As often as possible - once a month, once in 3 months, but not less often than once a year because new members of the team join in the meantime and need to be introduced to the team.
Formal regular communication is the most important for the business. This should occur in two ways: individual and in a team. The manager should take the time to organize regular meetings in a formal environment where employees can share ideas, can participate in decision making, can share feedback, can ask for advice or bring up negative issues concerning their own individual work or the team. Individual meetings should occur not less often than once in 2 weeks (preferably once a week) because the employee has a lot of tasks and he may need support with some and he can't wait for more than 2 weeks. Group meetings can occur a little less often, but not less than once a month. Normally team results are prepared at the end of the month so the beginning of each month is a good time to organize a team meeting.