Originally the ids were intended to be useful for linking different
information together internally, and for providing references
externally. However, they weren't used internally, for this, pointers
seamed to be more useful, as they also allow to directly access the data
and also have a relation defined.
Regarding reference purposes, they aren't really needed, and it is more
convenient to directly use some strings, and they aren't more
performant, as there still have to be internal checks and looking for an
int isn't more performant, then looking for a pointer.
Also, they have to be stored, so they need more memory and also some
code, to be handled.