As far as I know all variable frequency drives with vector control can also be run with just V/F control.
A drive in vector control mode has several tuning parameters to increase or decrease motor performance. With factory default parameters a VFD in vector mode will have higher performance than a drive in V/F mode. Sort of like a “sport or racing” computer option in a modern automobile.
Depending on the application using vector control can use a lot more power. If you have a rapidly surging load the vector may be really struggling to keep the speed constant while a variable frequency drive in V/F mode never notices the speed change. If the application has a steady mid-range speed and load or has a slow rate of change a vector and V/F may be very close in amp draw.
If you have an application where you need the vector for starting or stopping quickly but you are using a lot of current at speed you can change vector parameters to reduce the current. In some applications it is cheaper to oversize a V/F drive to get starting or stopping torque if you don’t need precise speed control.
I accept the fact that, in the practice, V/f is considered by many the better choice for fan loads, but I see few reasons why V/f approach could result in better efficiency.
One reason could be that, since it doesn’t try to regulate anything, practically it can’t oscillate due to weak stability, although oscillations may still occur (I’ve seen a heavily vibrating torque measurement on a fan driven by a V/f variable frequency drive).
Another could be that, while non-linear V/f curves (suitable to non-linear loads as fans) are quite common, the same is not done for the flux reference (magnitude) in vector control.
And, of course, the few parameters of a V/f control are far easier to tune than a vector scheme (which companies don’t really share).
However, one interesting thing that can be done with vector control is, for slow dynamics applications, to automatically tune the flux reference to achieve a minimum loss control during the control operation. I don’t think this would be possible with V/f.