One of the biggest problems in a PhD program is lack of students. More students means greater peer support. More students also means many events and activities are more cost effective (or less dollars per student).
Quick tip. If you're building a PhD program, don't be scared of having a large number of students.
One of the biggest problems that students face when they're doing their PhD, is lack of peer support. Lack of other PhD students to talk to about their work. So if you want to help alleviate that problem enroll more students. Obviously, if you do so make sure that you're clear to the student that the career that they might be going into, say an academic career, is not necessarily where they will end up. But if you want to have a good PhD program, you'll need plenty of students.