If you execute this command on a coil, then you will receive a set coil. Such a coil never overwrites the value TRUE in the respective Boolean variable. This means that once you have set the value of this variable to TRUE, it will always remain at TRUE. A Set Coil is designated with an "S" in the coil symbol.
If you execute this command once again, then you will be given a Reset coil. Such a coil never overwrites the value FALSE in the respective Boolean variable. This means that once you have set the value of this variable to FALSE, it will always remain at FALSE. A Reset Coil is designated with an "R" in the coil symbol.
If you execute this command repeatedly, the coil will alternate between set, reset and normal coil.