This command is used to remove an unwanted child from an object you own. If you owned said child, you could use @chparent; this command is to cover the other case, namely where you don't own the child.
Both forms of this command chparent <object> to its grandparent, provided you own the parent. The second form matches the string you supply for <object> against the list of children of the given <parent>.
Turning off the fertile bit (.f) for a particular object prevents others from creating children of it or chparenting to it (see "help @chmod").
Note also that, though the name might seem to indicate otherwise, this command does not change the ownership of any object.