Bonjour Julie !
So...
- Il faut partir
The obligation comes from an outside source : rule, law, time restraint...
- Il faut que tu partes versus Il te faut partir
In both cases, you want to emphasise who is being compelled here.
The Subjunctive option is actually the most colloquial and common here, whereas the second option is very formal and quite antiquated.
I hope that's helpful!
Bonne journée !
