Group work and Pair work

I want to speak the group work and the pair work today.
What are the advantage and the disadvantage though the group work and the pair work are multiused as an activity of the class of English?I want to think.

Merit of group work and pair work
･The student enthusiastically acts.
･Opinions each other can be exchanged.
･It is easy to say my idea.
･The concentration to the class increases.
･The understanding level of the class goes up.

Weak point of group work and pair work
･It is not possible to jump aboard by concentrating if the content of the activity cannot be understood.
･It matches it to other people's opinions.
･It becomes not connected.
･The classroom becomes annoying.

Correspondence prior of the teacher becomes and, anyway, correspondence after the fact becomes important. As prior correspondence, it clearly explains the content of the activity and the example is given if necessary. The content of the activity is reviewed as correspondence after the fact.

If I am an English teacher, I want to take the group work and the pair work to the class basing this merit and the weak point.