The most common indication for removed of impacted teeth is recurrent pericoronoitis, pain, infection, etc., pericoronitis is the inflammation of the gingival surrounding a crown of a partially erupted tooth, therefore in order to avoid food lodgement with pericoronal infection and pain, the ultimate solution is removal of impacted teeth.
(Note that chronic periodontal disease and orthodontic treatment also warrant removal of impacted teeth under specific conditions, but they are not the commonest.)