Why the magnetic flux produced in air gap of solenoid is usefull flux? ( leakage flux)?

Question

related to magnetic circuits

Answer 1

I can think of 2 reasons:

1. It all-but prevents the core from going into saturation if a DC current is applied to the solenoid.

2. A Hall sensor can be place in the gap to measure DC flux, resulting from DC current.  Hence a DC current sensor can be made.

.