You will find door a door closer almost every where from blocks of flats to offices, they play an important role in the safety of your property, whey will shut your door to make sure it is secure and they will prevent smoke from passing though room to room in case of fire, so please don,t discard them.
In most cases door closers can be adjusted but be sure to get a professional to do this as I have personally seen many broken beyond repair with the seals going.
I deal with most door closers, you have the Transom door closer which you will find on shop front doors, Overhead door closers, which are the most common type of door closer, the Floor spring which is concealed under the floor line, the Concealed door closer you will find on flat doors, and last the Spring closer which is probably the most unused closer.