Halliday & Matthiessen (2014: 502):
The non-finite clauses may occur with or without explicit Subject, e.g.
I just don’t see the point [[ × of having three or four different lists of people]] .
That’s the reason [[ × for keeping the sheets]] .
Soon the time came [[[ × for Kukul to take his place among the men of his nation]]] .
Sometimes the enhancing relation is marked by an explicit binder, e.g. why, where, when; here the Subject has to be implicit:
Chinchilli day is a reason [[ why to go to Las Vegas]] .
Carrasco, a place [[[ × where to return from work || and feel on holidays]]]