Yes, it can be useful to talk to the FT.
He can tell you if you have found all the supects.
For example, easy cases always have 5-6 suspects (people you can question)
But if you only have five, you can go to the FT, he will tell you either
A)Your journey nears its end for good or ill I cannot say. This means that you have all the people.
B) I sense that there are others with whom you must speak.
This means you need to find another suspect by asking for motives.
Blah, its not as complex as i make it sound!