Good airflow, will help keep your plants environment at optimal levels. For example, it will keep your temperatures and humidity in check. Also, good grow room extraction, will reduce the chances of rot, mold, and heat stress to your plants. So choosing the right size fans and extractor is important.
Also, a properly sized carbon filter is a necessity. However, if you buy the wrong one, you might as well not have one at all. Your security is priority, covering the smell is rule number 2! Break it, and you may suffer the consequences. In other words, do not cut corners with a carbon filter.