Correction of mistakes is a must, but it also depends on the purpose of the activity. If students have just been presented with the target language, then the initial opportunities for practice focus on accuracy. After all, students need to accurately produce the language.
However, elsewhere in the lesson, students need free(r) activities which allow them to experiment and personalize the material. It's often intrusive for the teacher to interrupt a discussion or role play, and so correction should be saved for after the activity.
Lastly, all mistakes are not created equal. Some language production may be above the level of the student, and so errors will appear. Correction here may not be desirable, because the problems remain above his productive level. The student won't understand the whys and hows of the problem, and at best will be limited to the most basic level of understanding, certainly not remembering or applying (as suggested in Bloom's Taxonomy).
I would also be cautious on correcting mistakes not related to the target language during the initial stages of the presentation/practice. As students are focused on the new language, small slips usually appear.
I wrote a few articles, which you can find here. These go into a lot more detail.
Correction & Feedback | Heads Up English | ESL Lessons
Chris Cotter
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